Screw guide

Screws - the Big Guide 

Whether you are a hobby craftsperson or an experienced professional - the subject of screws always raises a lot of questions. Like which types of screw are best suited for which application? What impact do threads types have on the application? And what differentiates a wood screw from a metal screw? 

So, in order to ensure the best result for each construction it is really important to use the right screws. This is the only way to create the best connection as well as a stable building component for all types of workpieces. The following guide will give you a comprehensive overview of screw types, application areas and the structure of individual screws.  Now it is really easy to choose the best screws for each project. 

Chipboard screws

The chipboard screw for fast and flexible processing.
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Wood screws

The powerful, approved screws for structural timber construction
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Full threaded screws

The fully threaded screws with intelligent solutions for demanding constructions
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Terrace screws

The high-quality screw assortment for the professional terrace assembly
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Special screws

The high-quality fischer screw range for special applications
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Facade screws

The special screw assortment for fixing wooden facades.
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Drywall screws

The extensive range of drywall screws for fastening drywall panels to all types of substructure
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Screw types - an overview by threads 

Screws can be classified by different criteria. Do-it-yourselfers might tend to consider only the application area. If, for example, wood is being used, you start looking for wood screws. It quickly becomes clear again that there are countless types of screws in this category. Which type and design is the right one really depends on the type of wood, among other factors. Do you work with a particularly hard or soft wood? Would you like a countersunk head for the screw? Perhaps different types of timber or wood materials have to be joined together? Even experienced craftspeople quickly reach their limits here. 

Therefore, it is a good idea to take a closer look at the threads of individual screws. Thread types are particularly suitable for specific areas of application allowing clean and trouble-free work with workpieces. 

Metric threads in particular are generally divided into external and internal threads. A fastening element with an external thread can be accommodated by a suitable interior thread. Self-tapping or self-drilling screws do not usually use threaded counterparts (such as nuts or threaded sleeves) - fastening is secured via the connection between the screw and the attachment to be connected.

The overview’s most important technical terms are: 

  • Thread outer diameter or nominal diameter: Denotes the maximum thread width in the screw’s longitudinal section or the maximum outside diameter 
  • Thread core diameter: Denotes the smallest diameter at the internal thread edge. 
  • Thread flank diameter: The distance between the profile centre lines of the two thread sides. 
  • Flank angle: The angle between two thread flanks. 
  • Thread pitch: Distance between the tips of the thread flanks after one turn. 
  • Thread: circumference of the entire helix of the thread. 

Only the area of the screw with a helical groove is designated as thread.It is called the shank when there is a smooth area above it.

Screws with metric threads 

The ISO metric thread is a standardized thread that uses a metric measurement. The metric thread has a 60° flank angle. Metric ISO-threaded screws are used world-wide. In the past, metric threads were used with slightly different measurements. In addition, there were also inch-threads. These have been replaced by the metric thread in most countries. However, there are still a few screws around with inch threads. 

Metric thread screws were standardized in 1996 via ISO 1502 (DIN: Metric ISO thread general application). They are set down in DIN standards DIN 13 and DIN 14. 

Metric thread screws are offered in a combination of screw and nut. Within screws, a distinction is made between types with standard (coarse) thread and fine thread. The flank angles and the thread pitch of fine thread screws are smaller than those of the standard thread screws. Screws with fine thread are very suitable for workpieces where there is only a small space for driving in the screw. The reduced flank distance increases the number of existing thread cuts and therefore the screw’s hold. 

In everyday language, screws with metric threads are also referred to as screws with metal threads. This is also the case even if the screws are made partly or completely out of plastic. The metal thread designation indicates that these screws are only used together with a screw nut. In comparison, universal screws or self-tapping screws, for example, cut their own threaded hole into the substrate. 

In addition to the different thread types, there are also several flank types. These can each be used within the thread forms. For example, there are screws with metric threads that have different flank shapes. The individual application area is often limited by the flank shapes: 

  • Pointed thread - suitable for precision work and general use 
  • Buttress thread - as a torque transfer thread 
  • Flat thread - formerly used as a transfer thread, hardly exists today 

Screws with split thread or double thread 

The double-threaded screws are especially used in wood construction. They are used as a version of fully threaded screws for connections or reinforcements as well as for fastening on roof insulation systems, especially when using pressure-soft insulation materials. This special type of wood screw convinces with its easy installation and increased efficiency. 

The thread enables axial load transfer. In direct comparison to a classic partially threaded screw, a higher tensile load is transferred and a high - pressure load is optimally absorbed. The screw uses two threads with different pitches. These threads compress the construction attachment when screwed in. So, it is not necessary to pre-load the attachment in order to create an optimized construction. Double threaded screws are therefore not only highly resilient, but also economical. 

These screws usually have a cylinder head which can be sunk almost invisibly into timber. At the same time, screw removal is easily possible. It is not a countersunk head - you can actually drive in the screw without splitting the wood. If fire protection is required for the construction project, these screws can be completely countersunk into the wood and then cover the head with a wood piece or cone plate - thereby already meeting some requirements of the current fire protection regulations. 
fischer ASL with double thread

Fully threaded screws 

Fully threaded screws are used in timber construction. The thread of the screw usually extends over the entire screw length. It starts directly under the screw head. The thread is able to absorb high tensile and compressive forces and distribute them evenly. Therefore, this type of wood screw is especially suitable for construction projects where wood components are under permanently applied force. These screws are also very well suited for reinforcing timber constructions. Larger dimensions are used for connections under high stress as well as for reinforcements. These screws almost always have a European Technical Assessment (ETA) indicating the respective load capacities. Bolt and screw manufacturers often offer dimensioning software for calculating load bearing capacity of the connection in question. 

Special chipboard screws are used for fastening wood-based panels (e.g. chipboard or OSB panels) and all types of wood such as hard wood. These are either fully threaded or also a partially threaded. These screws have a self-tapping thread or even a drill tip. They can be screwed into soft and most types of hard wood and chipboard or MDF boards without the need for pre-drilling. When using full-thread screws with a countersunk head, make sure that it is screwed flush with the surface of the wood, because a deep turn can split the wood. 

Partially threaded screws 

Wood screws are available with full and partial threads. Partially threaded screws are ideal for achieving a secure fastening between wooden boards and wooden beams. A partially threaded screw has a thread-free area right below the screw head, which is called the shank. The shaft length should be at least equal to the thickness of the wood panel to be fastened, so that the two components to be screwed together can be pulled together properly. 

Partially threaded screws are also available with countersunk head. Alternative head forms include a round head or a hexagonal head with a moulded washer. Wooden panels on walls or wooden beams for decks can be fastened together cleanly and evenly. If the screw does not have a self-tapping thread then pre-drilling is necessary. 

fischer chipboard screw with partial thread.

Screws with an internal thread 

Screws with internal threads are used especially often in furniture construction and therefore in timber processing. 

Screws with an internal thread are usually supplied together with a matching counterpart. There are also models that are suitable for screwing in with DIN standard threads. The screw has a traditional external thread which is used to fasten it to the workpiece. At the same time there is a hollow internal thread that can take on another screw. 

Some manufacturers offer combinations of two mating parts, which are only compatible with each other and are not standardised parts, therefore cannot be combined with other parts. This is frequently the case with special furniture screws. This type of screw is used to securely fasten together individual furniture parts. As a rule, however, they are metric standard threads. 

Internal threads are also often used for pipe threads. These are not screws in the traditional sense. The threads are directly cut into the pipe ends allowing easy connection between pipe sections. Both internal and external threads are available for this. The pipe threads can be self-sealing (conical or tapered) or cylindrical. In this case they are not self-sealing and require an additional sealant for the connection. 

Screws with inch thread 

Globally, metric screws are the most common utility screws. There are some markets where inch screws still hold their own today. Especially in the USA, where inch screws are widely used. Compared to a metric screw, the primary difference to an inch-threaded screw is the unit of measurement. 

One inch (English= inch) corresponds to 2.54 cm. If you want or need to work with inch screws, it is important to make the correct calculation before buying screws. This applies to screws with fine and coarse threads. 

There are various thread types for inch screws. The following are the most common in the world-wide market. 

  • UNC – US American standard thread. The coarse thread was formerly designated as NC. 
  • UNF – US American standard thread. The FINE thread was formerly designated as NC. 
  • British Whithworth - threads (e.g. BSP, BSW und BSF) – Whithworth threads have a 55° flank angle. The metric screws have a 60° flank angle. 

UNC and UNF threads also have a 60° flank angle, but have a different diameter than metric screws. Therefore, metric screws, American inch screws and British inch screws are not compatible with each other. 

Regardless of the inch screw’s thread type, the length of the screws is always designated in inches or mm. The thread diameter, on the other hand, is only designated as a fraction. Inch is denoted by the special character ". A thread with ¼" therefore has a diameter of 6.35 mm (= 1/4∙2.54).

Screws without a thread 

There aren't any thread-less screws in the true sense of the word. This type of screw refers to pairs of screws, which are composed of a standard screw and a screw with internal thread. The screw connection is secured by bringing the two parts together. 

These models are available in very different lengths and designs. So, you will find offers for each screw head. Some counterparts can be screwed into the screw without an external thread, others come in the form of a nut and are turned at the lower end via a short- threaded piece. 

Again, these are mainly screws from the furniture industry. The head of the screw often disappears and is flush in the pre-drilled holes. Unthreaded screws with a short counterpart usually use a fine thread. This provides a high level of security despite the short connecting piece. 

Cap or socket head screws 

Cap (cheese head) screws, also known as socket head screws, are used in application areas with special construction requirements. If the screw head is difficult to access due to the construction of the workpiece, socket head (cap) screws are the right choice. In most cases, the workpiece usually has the same dimensions as the screw head. Which specific product requirements the socket (cap) head screw has to meet depends on the building attachment. 

The range of socket head screws is extensive. Models with low head height or versions with a slotted drive are available. There are also socket head screws and they comply with the metric DIN standard. You also have the choice between fully threaded and partially threaded. 

It is possible to have made to order products manufactured. The screw’s dimensions are then perfectly adapted to the workpiece to be fastened. However, made to order is rarely used in the private sector. The screws are available in the usual standard lengths. 

  • 0 – 45 mm 
  • 46 – 75 mm 
  • 76 – 110 mm 
  • 111 – 200 mm 

They can be used in many ways and are particularly suitable for connecting different metals such as galvanised and ungalvanised steel and stainless steel

Cap screws in use

Screws with drill points 

Another special feature in the screw range are screws with drill points. These screws have a pronounced point which, as the name suggests, is perfect for drilling into a workpiece. The basic shape is similar to that of a classic drill. As a rule, the drill tip has two cutting edges. The drill point screw works very well for fastening metals or plastics. This type of screw is regularly used for fastening window fittings. 

The drill tip screws can be found in various design combinations.

  • Metric threads 
  • Inch threads 
  • Various drives 
  • Different head shapes 

The starting point for the tool, the bit, is known as the screw drive. The most popular forms are the cross-slot drive and slot drive – caution the slot drive is not suitable when used with power screwdrivers, because there is not centring and the screw wobbles when screwed in. Additionally, there are also the hexagon socket, the external hexagon, the inner star TX (or Torx) or the square drive. 

fischer Powerfull with drill point and TX-drive. The drill point enables a screw connection without pre-drilling and provides guidance when screwing in.

Special screws

Special screws are particularly used in industry and in specialist trade. These are optimized to accommodate special features for various workpieces or constructions. The best solution is quickly found by using the right special screw, whether for a very high tensile load that has to be borne or a screw within a construction that is difficult to reach.

It is also possible to have made to order screws produced. This approach is primarily used for large projects. For the private sector or for use in small and medium-sized companies, the cost for custom-made products is just too high. Therefore, there are some special screws which are offered in standard shapes and sizes. 

Adjusting screws 

Adjusting screws are used for connecting timber components. Underneath the screw head are thread-less grooves. When an adjusting screw is screwed in, these grooves hook into the workpiece to be attached. This provides a secure hold in the work piece to be mounted. Even when the screw is loosened a little anticlockwise to make an adjustment, the connection still remains secure due to the adjustment grooves. 

Another benefit of an adjustment screw is the self-tapping thread. Time consuming pre-drilling is not necessary. 

Hanger bolts 

The hanger bolt has a wood thread at one end. A metric thread is on the other end of the hanger bolt. The hanger bolt is used, among other applications, to secure a workpiece using a nut to natural stone, wood or even concrete. 

Lag screws/bolts 

Lag screws also fall into the category of special screws. These are screws that can be fastened either using a wrench or a socket wrench. Lag screws comply with DIN 571 and are also known under other names: 

  • Hexagon head wood screws 
  • Galvanised screws 
  • Vienna screws 

The lag screw's thread does not start directly below the screw head. There is a smooth shaft below the head. The partial thread ensures that high pressure is reached between the building components to be connected. If, for example, two boards are screwed together, the lower wood component is pulled securely against the upper one. 

The lag screw is a traditional timber screw. The hexagonal screw head makes retightening easier. The screws are also available in stainless steel. To be used correctly, lag screws must always be pre-drilled in two steps into the wood. 

Lag screws are available in galvanised and hot-dip galvanised steel. 

Security screws (tamper-proof)

The primary difference between these screws and conventional screws is their special drive. You can buy the right bits from your hardware or DIY shop if you need to open and or remove this special screw. The most common screw drives for special screws are the following:

  • Hexagon socket with pin
  • Torx with pin
  • Interior multi
  • One- way slot
  • Tri-Wing
  • Torq-Set
  • Pentalob
  • Spanner/wrench (two-hole drive)
  • Bristol

A one-way screw cannot be removed using a normal tool. The drive flanks are flattened in the return drive and do not provide a support surface for a drive tool. If it is necessary to remove them, there are special tools such as a left-turning screwdriver.

Special screws are always used for applications where screw connections must be tamper-proof and unscrewing the screw must be prevented as much as possible. Vehicles in public transport are a classic example. Electrical appliances manufacturers increasingly rely on special screws to prevent customers from carrying out dangerous repairs themselves. Children's toys that use potentially hazardous components inside also have special screws.

Depending on the type of security screw, models are available with pan (raised) head, flat head or countersunk head. 

Self-tapping screws 

A self-tapping screw can cut its own thread into a material. This type of screw is used in many applications and area because it is suitable for working on wood, metal and plastic. 

These screws are available in two versions: Thread-cutting screws and thread-forming or thread-rolling screws. A thread-forming screw has a blunt end. A thread-cutting screw has a pointed end. Accordingly, both types are handled differently. 

To insert a thread-forming screw into a material, pre-drilling is required. This is especially true when a tapping screw is used in sheet metal. On very thin sheet metal, you can mark the drilling location with a centre punch making it easier to drill into the workpiece. For thicker sheet metal and steel, however, it is essential to make a proper pilot hole. Always choose an upper attachment for a pilot hole that is approx. 2 mm smaller than the screw. However, for smaller or larger diameters, precise specifications for the pre-drilled diameter need to be observed. 

A thread-cutting or also a self-tapping screw with a tip is screwed into the workpiece without any pre-drilling. These screws are very popular in woodworking and furniture construction. They can be inserted easily and quickly into very different materials. At the same time, disassembly is possible at any time.  

Screw head: when to choose which? 

Not only does the thread play a role in choosing the right screw, but the screw head must also be considered. It is of course important that you have the right tool for the screw head and the screw drive at hand. In addition, the different heads are more or less suitable for certain areas. 
Traditional screws for home use have a flat head with a slotted or cross drive. However, slotted screws are falling out of favour, as the lack of screw bit centring when screwed in can often cause minor injuries or at least a bother. For both screws, however, almost everyone has the right tool. Simple screw connections can then be easily carried out between workpieces or for wall mounting. The anchors are also important for good load transfer in solid or drywall construction. You will find all important information about screw anchors in our large anchor guide (link to anchor guide). 

Below is an overview of the most common screw heads and screw drives as well as the relevant areas of application. 

Screws-drives/ screw profile 

The screw drive or screw profile designates the attachment on the screw head that is inserted into the tool (bit and then bit holder). Usually, a manual or power screwdriver is used to drive the screw in. Nowadays it is usually a cordless screwdriver. 

There are well over 100 different screwdrivers. Many of them are used in industry or house construction. Others are country-specific and are therefore regionally limited to the most common application. From a global perspective, the slot, cross slot (Philips) and Pozidriv (cross recess) drives are particularly widespread. Also, the inner star TX- drive or also the Torx, are very common. 

There are many screw drives as inner drive and outer drive. For example, a triangular socket is set over a triangular drive and the triangular bit is inserted into a triangular drive. When choosing screws, it is therefore essential to pay attention to which tool you have available. A comprehensive tool kit ideally contains the necessary bits and nuts. 

Croossot, Phillips and Pozidriv 

One of the oldest and also best- known models is the Phillips screwdriver. This is the most often used screwdriver in households. Before its market launch, the simple slotted drive was the only available screw driver. The cross-head was the next development of this basic screwdriver type. The easier drive and torque transfer were able to quickly convince the end-users. 

Around 1920, the Philips drive was first introduced to the market. Basically, this was also a cross-head drive, but the torque was considerably improved. In addition, the design of the drive allows for automatic centring of the screws. Another major improvement in drives ultimately led to the Pozidriv. This model's excellent torque transfer makes work much easier. For screw connections with normal requirements, the Pozidriv screws are the best choice for applications in homes. 

Torx- the drive for professionals 

A Torx drive is a registered brand-name product. However, there are also no-name versions on the market. The Torx drive is very popular especially in professional trades. It is an optimization of Pozidriv and Co. The star-shaped drive offers a number of advantages. 

  • High torque 
  • Stable centring 
  • No slipping (cam out?) 
  • No spinning 

Hexagon - the sturdy classic 

For a hexagon head screw, the screw head is also the drive. The great benefit of this drive is that the screw can be gripped from all sides. Therefore, it is also suitable for mounting in places that are difficult to access. 

Today, hexagon head screws are also increasingly used as decorative features in furniture construction. 
The different drive types of screws

Screw head shapes 

The choice of a suitable screw head dictates both functionality and appearance. The selection is extensive, and the individual heads have quite different advantages as well as disadvantages: 

  • Flat round head (e.g. for carriage or coach screws/bolts): The screw head does not have a separate drive and screw is fastened by means of a nut. This is ideal for achieving particularly secure screw connections, for example on playground equipment. 
  • Raised countersunk or mushroom head: This screw head is a true classic. The countersunk part of the head is recessed in the attachment part and the upper half of the "lens" shape protrudes over the attachment part. This head shape is often chosen because of its aesthetics. The rounded head also reduces the risk of injury. 
  • Pan-Head or round head: This head has a flat under-head shape and is not countersunk in the attachment part at all. It protrudes over the attachment part at full head height. This head shape is almost always used to attach metal sheets or plastic components. These are practically never used to attach wood parts. 
  • Countersunk head: Countersunk head screws are used in all forms. Wood screws, metal screws or special screws use this design. The benefit is that the head can be countersunk flush with the surface of the material. In addition, the countersunk head is offered with all common drives from Torx to Phillips (cross recess drive). 
  • Flat head: A wood screw often has a flat head. You do not have to use washers with these screws to ensure an even torque transfer. Flat heads are aesthetically appealing and therefore are often used in wooden constructions. Due to the bigger head diameter, these screws installed in wood can bear higher loads than e.g. countersunk screws because the resistance against head pull-through is significantly increased. 
  • Socket (cap) head: Socket head screws are widely used in metal construction. They can be used from both the side and the top. They are ideal to deliver the best possible performance also in industrial environments. 

Screw length 

In order to securely connect workpieces together, the screw must have the appropriate length. If it is too short, a secure hold is not possible. If it is too long, it protrudes from the workpiece. Depending on the screw's head shape, for each shape the length is measured slightly differently. 

A screw with countersunk head is measured in its entire length - from the beginning of the head to the tip. A screw with a protruding head, for example a pan head or flat head, is measured from the bottom of the head to the tip. When purchasing screws, consider not only the thickness of the workpiece, but also whether you are using an anchor, washer or nut. There are also many combinations of length and diameter of screws. 

Screw diameter 

The screw diameter is measured at the thread. This value indicates the widest thread diameter of the screw. The diameter of the screw is important for many applications. If pre-drilling is required, the correct size for the drill is selected by using the screw diameter. 

Especially with wood screws, an incorrectly selected diameter can cause issues. If the screw is too thick, the risk of splitting the wood is too high. Therefore, in general, always pre-drill larger screws in the wood, even if the thread is self-tapping, unless the edge distance and the wood thickness and width are large enough. 

The screw material 

The range of different screw materials is constantly growing. There are even mixed material types composed of several materials. However, since certain requirements such as tensile strength or corrosion protection usually play a major role, some materials are used particularly frequently: 

  • Stainless steel 
  • Steel (often hardened) and usually galvanized and passivated or hot-dip galvanized 
  • Plastics 
  • Aluminium 
  • Brass

Stainless steel screws and steel bolts provide high strength. Stainless steel screws are extremely weather resistant. And they are inexpensive to manufacture. Brass screws are beautiful looking and provide even better corrosion protection than e.g. galvanized steel screws. Steel screws and other metal screws are used in private households as well as in industrial areas. 

Plastic screws are often marked with PA: for polyamide. These screws are easy and inexpensive to produce. In addition, they have a high degree of flexibility. Unfortunately, they are not particularly temperature-resistant and not able to bear high loads

Which screw for which material? 

You also have the choice between wood, metal and also universal screws. Moreover, there are special designs within the range of screws that are optimized for specific applications. From thread to material to drive, these screws are aligned to the individual conditions of each workpiece. Strength class also plays an important role. Metal screws are subjected to greater stress during processing than, for example, wood screws. In the following are special features of some types of screws for certain materials. 

Screws for plaster boards

Gypsum fibreboards, also known as Fermacell boards are used in dry construction, whenever the building construction has to fulfil exacting requirements. These stable boards are therefore well suited for high shear loads and fire exposure. Compared to plasterboard, gypsum fibreboards are heavier and at the same time much more durable.

Fastening to a substructure requires just a little effort. The choice of the right screws is especially important. Special drywall screws and Fermacell drywall screws have a self-tapping tip and are used without the need for pre-drilling and anchors. The screw thread is often a HiLo double thread (one thread protrudes slightly more than the other over the core diameter of the screw). The screws are available loose and in strips (for a faster screwing -in using an automatic feed gun to drive many screws in a series). 

Screws for plaster boards 

Plasterboards, also known as sheetrock, are light and easy to install. They are also really inexpensive to purchase. Sheetrock is perfect to quickly clad walls and ceilings. These are also known as drywall walls or ceilings. Special drywall screws are used to fix the boards to the metal or wooden substructure. In relatively soft material such as wood, it is best to use a coarse threaded screw. Finely threaded drywall screws (S-type screws) are used for fastening onto metal substructures (for metal stud walls). Usually, there pre-drilling is not needed. The screws are also available loose and in strips (for faster screwing in using an auto-feed screw-gun to drive many screws in series). 

Wood screws 

The thread of a wood screw has been optimized to be easily screwed into all kinds of woods. It exerts low splitting force, which is especially advantageous for small edge distances and for thin wood panels, as well as for harder wood types. If the screw does not have a self-tapping thread, you should always pre-drill the substrate (e.g. for lag screws/bolts according to DIN 571). If you are connecting different materials, for example steel and wood, it is also important to consider the type of screw head. If the screw head sits on the steel and the thread is screwed into the wood, a countersunk head is unsuitable, since a countersink needs to be made in the steel component. A flat plate or hexagonal head screw (the latter also with a moulded-on washer), as with a normal metal screw, is then the right choice. 

Screws for MDF (medium density fibreboard) 

MDF boards are medium-density wood fibre boards pressed together from a combination of wood, glue and water. The board does not have a grain pattern. Never directly screw into the MDF board, it is better to pre-drill all holes into the board. Without pre-drilling, the risk of splitting the board becomes too high. 

Thick MDF boards can be fixed quite easily using a partially threaded screw. 

Chipboard screws 

The chipboard screw can be a universal screw or a wood screw with countersunk head. There is no need to pre-drill the attachment. The chipboard screw's sharp tip easily cuts directly into the material without a lot of resistance. 

Metal screws (self-tapping?) 

Self-tapping screws have a hexagon head, raised countersunk head or a pan head. There are no countersunk head types. The thread is especially hardened and is able to cut into the substrate without pre-drilling. The self-tapping screw is made of robust steel or stainless steel, and you can get models with cross-head or hexagonal drive, among others. Many metal (self-tapping) screws also have a drill tip. 

Screws in concrete 

When you want to drive screws into concrete, there has been for some time a popular alternative to metal expansion anchors, heavy-duty anchors and others: a concrete screw is screwed directly into the substrate without anchors and without a loss of load-bearing capacity. The thread of the screw has special toothing, which cuts an additional internal thread into the drill hole. Only pre-drilling is required to use the concrete screw properly. Then the steel or stainless-steel concrete screw is simply tightened using an impact driver (tangential impact driver) or in exceptional cases by hand. 

Drywall screws (plasterboard or gypsum fibreboard screws) 

Drywall screws are mainly used in drywall construction. There are versions with or without drill tip. The drill tip is especially suitable for applications on metal substructures without having to pre-drill there. You can get screws with fine thread (for metal substructures) and coarse thread (for timber substructures). Many types are also available as auto-feed screws. Screws with double or HiLo threads (one thread protrudes slightly more than the other over the screw’s core diameter) are ideally suited for good installation and load-bearing capacity in plasterboard (Fermacell boards). 

Which screws are suitable for anchors? 

If you want to use anchors, then screws and anchors must be compatible with each other. It is possible to buy screws and plugs as a set, however you can often easily put the two mating parts together yourself. The choice of anchor is determined by whether you are going to drill or fasten to a wall or ceiling. The material of the substrate is also important. For aerated concrete, for example, you need a different plug than in concrete. Basically, you can get screws combined with universal anchors, special anchors and cavity anchors. 

You can calculate the correct screw length by adding the anchor length, the workpiece thickness to be fastened and the screw diameter. You can also easily determine the appropriate screw diameter. 

  • 6mm -anchor  Ø6 mm - drill 6 mm for the hole - screw diameter: 4-5 mm 

  • 8mm- anchorØ8 mm – drill 8 mm for the hole – screw diameter 4.5-6 mm 

  • 10mm- anchor Ø10 mm – drill 10 mm for the hole – screw diameter 6-8 mm 

How many screws are needed?

So, you are planning a construction project and want to order all materials in time. The following gives you an overview of the number of screws you need for various connection challenges. 

How many screws per deck board? 

To secure a deck board, as a rule use two screws per board at the crossing point with the substructure. For particularly long deck boards, the number of screws depends on the number of structural beams underneath. The spacing between the beams in the substructure must therefore be designed so that the deck boards do not bend too much and the deck boards are able to bear the load. 

How many screws per OSB board? 

The OSB boards are available in standard dimensions of 2500 mm x 625 mm or 2500 x 1250 mm. In addition, the boards are available in different thicknesses. They are easy to lay and are highly suitable as a moisture barrier, among other factors. When the boards are screwed to a substructure, the axial distances between the beams or posts should not exceed 62.5 cm. Some boards (known as flooring boards) have a tongue and groove all around. If the boards do not provide a structural load-bearing function for the stability of the building, a general screw spacing of 10 - 15 cm is specified for each linear intersection with beams or posts (uprights) of the structure. 

How many screws per2 m for plasterboards? 

To ensure a secure hold for plasterboards, the distance between the screws should not exceed 25 cm. Depending on how the substructure is constructed sometimes more or fewer screws are used. The screw’s distance to the edge of the board should be around 15 mm. In general, it is better to use too many screws than too few. This is especially true for fastening panels to the ceiling and for thin panels. 

Screws - strength classes 

The screw's strength class for metric screws of hardened steel is indicated by a number combination of two values. The two numbers are simply separated by a point. The first number denotes the index value of tensile strength / 100. The second number denotes the index value of yield strength as the ratio of yield strength to tensile strength. 

  • Tensile strength: What is the maximum tensile force the screw material can withstand without breaking? The screw can become permanently deformed (elongated). The unit is N/mm². 
  • Yield strength: Specifies the stress in the screw (unit N/mm²) up to which it behaves elastically, i.e. it returns to its original length after being subjected to a load. 

Loosening broken screws 

If the screw is damaged, it is not easy to loosen it. Using a couple of simple tricks, you can also remove stuck screws. 

  • Use gripping pliers to remove slightly protruding screws 
  • Place a rubber band over the stripped screw and firmly insert the screwdriver into the stripped screw using slow, firm pressure to extract the screw 
  • Slightly damaged screws can be removed with an impact driver and the appropriate bit 
  • Use a special screw extractor set to cut a counter-rotating thread in the screw head 

Screws without pre-drilling 

Whether screwing in without predrilling is possible depends on many factors. Not every thread is suitable, among other considerations. If a wood screw does not have a self-tapping thread, you cannot avoid pre-drilling. Especially if the wood is quite thin and you are fastening using a thicker screw close to the edge. Otherwise the risk of splitting the wood is too high. 

You must always pre-drill in concrete and almost always pre-drill in metal. Only thin sheet metal and plastic can be fastened using the appropriate special screws without pre-drilling. If screws with a drill bit are used, then it is also possible to screw into somewhat thicker metal without pre-drilling. 

Removing rust from screws 

If rust builds up on a screw, there are various ways to remove it. Rust converters are particularly easy remedies. These chemical agents are available in a gel, paste or spray. Depending on how severe the rust is, chemical rust removers are really suitable for large and small surfaces. If a small metal screw is rusted, an old household remedy can often help: simply treat the surface with vinegar or citric acid. 

Electrolysis is a good method for dissolving large amounts of rust without a lot of effort. To do this, just fill a plastic bucket with water and add four tablespoons of sodium bicarbonate per litre of water. Use a piece of steel as an anode. Use a piece of magnetic material that is in the water as the sacrificial anode. Connect the positive pole of a charger to the sacrificial anode. Connect the other pole to a rust-free part of the metal piece to be treated and immerse it in water. It may take up to 24 hours for the rust to completely dissolve.