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.
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.
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.
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:
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.
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.
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 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).
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.
They can be used in many ways and are particularly suitable for connecting different metals such as galvanised and ungalvanised steel and stainless steel
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.
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.
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.
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:
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.
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:
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.
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.
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:
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 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
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).
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.
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.
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.
If the screw is damaged, it is not easy to loosen it. Using a couple of simple tricks, you can also remove stuck screws.