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Types of Screws - A Thomas Buying Guide
Screws are a versatile form of mechanical fastener that is available in a wide variety of specialized types.
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Screws are a form of mechanical fastener that features an external thread, and which are capable of securing objects together by the application of torque to the screw head to drive the fastener into the two materials being joined. Unlike bolts, which are also externally-threaded fasteners, most types of screws do not utilize a mating nut and washer to attach or join the objects together, meaning that the action of driving the screw through both objects creates a mechanical joint of sufficient strength to bond the objects together. However, there are exceptions to this general concept, and some of the types of screws discussed in this guide are, in fact, designed to mate with a matched threaded element.
The primary types of screws include:
Barrel Screws
Cap Screws
Captive Screws
Concrete Screws
Deck Screws
Dowel Screws
Drive Screws
Drywall Screws
Framing/Self Drilling Screws
Machine Screws
Set Screws
Sheet Metal Screws
Shoulder Screws
Thread Forming/Thread Cutting Screws
Thumb Screws
Weld Screws
Wood Screws
In the sections below, each of these types of screws is defined and explained. It is important to note that there are other varieties of screws with connotations outside of the category being considered here, which deals with the fastener variety. As an example, ball screws which are a form of linear actuator, do not function as a fastener and hence are not included as a type of screw within this guide.
For related information on bolt style fasteners, consult our guide covering types of bolts.
Barrel Screws are the externally threaded components of two-part fastening systems. The barrels are the internally threaded nut components. Barrel screws are used primarily for binding two objects together. The barrel of the system is typically available in various lengths to accommodate various thicknesses. The screw mates with the barrel and is tightened thus securing the objects to each other. Various head styles, materials, and finishes are available depending on the application.
Cap Screws are threaded fasteners with heads in a variety of styles such a hex, fillister, etc. and with drives in a variety of styles such as hex socket, slotted, etc. which are used with tapped holes or threaded nuts. Cap screws are used primarily for assembly purposes in machinery. Cap screws based on the type of head include button head, flat head, etc. Cap screws can be fabricated from metals and non-metals depending on the application.
Captive Screws are threaded fastening systems in which the screws are secured within the mating parts so they stay with the mating parts when loosened. Captive screws are used primarily for securing panels and similar access ports which are subject to frequent removal and reinstallation.
Concrete Screws are threaded fasteners with specially designed threads for drilling and holding in concrete. Concrete screws can be coated with adhesives for increased holding ability or lubricant for ease of driving as required. Different head styles are available as well as many different materials depending on the application.
Deck Screws are threaded fasteners where the threads are significantly larger in diameter than the shanks and are specifically designed for the construction of decks. Deck screws are used primarily for the construction of wood or engineered wood decks. They are specifically designed to easily drive through wood decking and secure into the deck joists. Deck screws usually have countersunk heads for flush finishing.
Dowel Screws are threaded fasteners with lag threads on their ends. Dowel screws are used primarily to fasten wood or other soft materials together while hiding the screws themselves within the material. They may have the same threads on both ends, or the threads can be different, and they may be fully or partially threaded depending on the application.
Drive Screws are threaded fasteners with a large angle helical threads that are designed to be driven into materials with impact tools. Drive screws are used primarily in heavy-duty fastening applications and can be used in castings, both ferrous and non-ferrous, as well as in plastic and sheet metal applications. The use of drive screws allows for speed in assembly as well as for high-strength assemblies.
Drywall Screws are fasteners with aggressive threads and sharp points which allow for self-threading through drywall (wallboard) and into the wood or metal studs behind it. Drywall screws are used primarily to secure drywall to the studs or framework of buildings.
Framing/Self Drilling Screws are fasteners with special points that allow them to self-drill holes before the threads engage. Framing/Self Drilling screws are used primarily for framing in wood or metal structures. This ensures a more accurate and faster assembly. Many different heads and drive styles are available depending on the application.
Machine Screws are fully threaded fasteners intended to be secured into tapped holes or with nuts. Machine screws are used primarily in the assembly of machinery. They are available in many different thread sizes, lengths, head and drive types, materials, and finishes.
Set Screws are threaded fasteners used for securing hubs to shafts. Set screws are available in a range of tip styles including cup, cone, dog point, and knurled, and come in various drive types.
Sheet Metal Screws are threaded fasteners that have sharp tips and threads which enable them to pierce and cut into sheet metal. Sheet metal screws are used primarily for binding sheet metal to sheet metal but can also be used to attach sheet metal to wood, fiberglass, or plastic. The piercing and self-drilling features eliminate the need to pre-drill and align the parts being assembled. The heads can be of different configurations including round or flush and of different drive types depending on the application.
Shoulder Screws are headed fasteners with tightly toleranced cylindrical shanks which work as bearing surfaces. Shoulder screws are used primarily for revolute joints, linkages, or sliding mechanisms. The main shank, or shoulder, is typically a precision machined feature to allow proper fit to the mating part with various grades available. There are a wide range of uses including pivots, bearing mounts, spring guides for punch and die sets, etc. and they are used extensively in industries ranging from aerospace to consumer goods.
Thread Forming/Thread Cutting Screws are threaded fasteners with specially designed tips and threads to allow them to cut or form their own threads as they are driven into holes. Thread forming/thread cutting screws are used when higher stresses within the assembled materials cannot be tolerated. The tip is specially designed with metal cutting edges. When stress can be tolerated and a higher holding force is required, so-called thread rolling screws are used so that they will deform, as opposed to cutting, the material.
Thumb Screws (also spelled as thumbscrews) are threaded fasteners designed to be turned by hand. Thumb screws are used primarily when a lower holding force is required and for temporary use where they are tightened and loosened frequently. They are available in various head styles such as knurls or wings and may even have slotted or Phillips style driving features for use with tools.
Weld Screws are threaded fasteners designed to be permanently attached to metal surfaces by welding to form threaded protrusions on sheet metal and similar materials. Weld screws, once secured in place, are used to attach other items that are then held with nuts. Various thread sizes and lengths are available as well as materials depending on the application requirements. The head style depends on the application and welding process.
Wood Screws are threaded fasteners with aggressive threads designed to be driven into wood. Wood screws use self-tapping threads which bite into the wood. Pilot holes are normally used to prevent splitting. The head of a wood screw is usually flat but others such as round, oval, or fillister are available.
Besides the primary types of screws listed above, other types exist for specialized uses. For example, tamper resistant or tamper-proof screws are designed to utilize unusual or uncommon methods of driving and removing the fastener, therefore requiring specialized tools and drive bits that are not commonly available. A common example of the use of these screws is in the panels used in public restrooms. Another type of specialized screw is quarter-turn screws, which as the name implies, is released after rotating the fastener through a 90o rotation.
This article presented a brief summary of some of the types of screws commonly used. For more information on related products, consult our other guides or visit the Thomas Supplier Discovery Platform to locate potential sources of supply or view details on specific products.
