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A machine screw is generally a smaller fastener (less than 1/4 inch in diameter) threaded the entire length of its shaft that usually has a recessed drive type (slotted, Phillips, etc.). Machine screws are also made with socket heads, in which case they may be referred to as socket head machine screws.
Sheet Metal Screw (Self-tapping Screw, thread cutting screws) - Has sharp threads that cut into a material such as sheet metal, plastic or wood. They are sometimes notched at the tip to aid in chip removal during thread cutting. The shaft is usually threaded up to the head. Sheet metal screws make excellent fasteners for attaching metal hardware to wood because the fully thread shaft provides good retention in wood.
A set screw is generally a headless screw but can be any screw used to fix a rotating part to a shaft. The set screw is driven through a threaded hole in the rotating part until it is tight against the shaft. The most often used type is the socket set screw, which is tightened or loosened with a hex key or hex driver.
Socket Cap Screw – Also known as a socket head cap screw, socket screw or "Allen bolt," this is a type of cap screw with a hexagonal recessed drive. The most common types in use are fitted with a cylindrical head whose diameter is nominally 1.5 times (1960 series design) that of the screw shank (major) diameter. Other head designs include button head and flat head, the latter designed to be seated into countersunk holes. A hex key (sometimes referred to as an "Allen wrench") or hex driver is required to tighten or loosen a socket screw. Socket screws are commonly used in assemblies that do not provide sufficient clearance for a conventional wrench or socket.
Wood Screw – Generally has an un-threaded portion of the shaft below the head. It is designed to attach two pieces of wood together.
Lag Screw (Lag Bolt) – Similar to a wood screw except that it is generally much larger running to lengths up to 15 inches (381 mm) with diameters from a quarter inch to 1/2 inches (6.4 mm-12.25 mm) in commonly available (hardware store) sizes (not counting larger mining and civil engineering lags and lag bolts) and it generally has a hexagonal head drive head. Lag bolts are design for securely fastening heavy timbers (post and beams, timber railway trestles and bridges) to one another, or to fasten wood to masonry or concrete.
Self-drilling screw (Teks(R) screw) - Similar to a sheet metal screw, but it has a drill-shaped point to cut through the substrate to eliminate the need for drilling a pilot hole. Designed for use in soft steel or other metals.
Drywall screw - Specialized screw with a bugle head that is designed to attach drywall to wood or metal studs, however it is a versatile construction fastener with many uses. The diameter of drywall screw threads is larger than the shaft diameter.
Particle Board Screw (Chipboard Screw) - Similar to a drywall screw except that it has a thinner shaft and provides better holding power in particle board.
Deck Screw - Similar to drywall screw except that it is has improved corrosion resistance and is generally supplied in a larger gauge.
Double ended screw (Dowel screw) - Similar to a wood screw but with two pointed ends and no head, used for making hidden joints between two pieces of wood.
Screw Eye(Eye Screw) - Screw with a looped head. Larger ones are sometimes call lag eye screws. Designed to be used as attachment point, particularly for something that is hung from it.
Cap Screw – In places the term is used interchangeably with bolt. In the past the term, cap screw was restricted to threaded fasteners with a shaft that is threaded all the way to the head, however this is now a non-standard usage.
Hex Cap Screw – Cap screw with a hexagonal head, designed to be driven by a wrench (spanner). An ASME B18.2.1 compliant cap screw has somewhat tighter tolerances than a hex bolt for the head height and the shaft length. The nature of the tolerance difference allows an ASME B18.2.1 hex cap screw to always fit where a hex bolt is installed but a hex bolt could be slightly too large to be used where a hex cap screw is designed in.
Self Tapping Machine Screw – Similar to a machine screw except the lower part of the shaft is designed to cut threads as the screw is driven into an un-tapped hole. The advantage of this screw type over a self tapping screw is that if the screw is reinstalled new threads are not cut as the screw is driven.
Stud - similar to a bolt but without the head. Studs are threaded on both ends. In some cases the entire length of the stud is threaded, while in other cases there will be an un-threaded section in the middle. (See also: screw anchor, wedge anchor.)
Shoulder Screw - Screw used for revolving joints in mechanisms and linkages. A shoulder screw consists of the shaft, which is ground to a precise diameter, and a threaded end, which is smaller in diameter than the shaft. Unlike other threaded fasteners, the size of a shoulder screw is defined by the shaft diameter, not the thread diameter. Shoulder screws are also called stripper bolts, as they are often used as guides for the stripper plate(s) in a die set.
Thumb Screw – A threaded fastener designed to be twisted into a tapped hole by hand without the use of tools.
Thread rolling screws - have a lobed (usually triangular) cross section. They form threads by pushing outward during installation. They may have tapping threads or machine threads.
Hanger Screw – A headless fastener that has machine screw threads on one end and self tapping threads on the other designed to be driven into wood or another soft substrate. Often used for mounting legs on tables.
Tamper Resistant Screws
Many screw drives, including Phillips, TORX, and Hexagonal, are also manufactured in tamper-resistant form. These typically have a pin protruding in the center of the screw head, necessitating a special tool for extraction. In some variants the pin is placed slightly off-center, requiring a correspondingly shaped bit. However, the bits for many tamper-resistant screw heads are now readily available from hardware stores, tool suppliers and through the Internet. What is more, there are many commonly used techniques to extract tamper resistant screws without the correct driver — for example, the use of an alternative driver that can achieve enough grip to turn the screw, modifying the head to accept an alternative driver, forming ones own driver by melting an object into the head to mould a driver, or simply turning the screw using a pair of locking pliers. Thus, these special screws offer only modest security.
The slotted screw drive also comes in a tamper-resistant one-way design with sloped edges; the screw can be driven in, but the bit slips out in the reverse direction.
There are specialty fastener companies that make unusual, proprietary head designs, featuring matching drivers available only from them, and only supplied to registered owners. An example of this would be the attachment for the wheels and/or spare tires of some types of car; one of the nuts may require a specialized socket (provided with the car) to prevent theft.
The break away bolt is a high security fastener that is extremely difficult to remove. It consists of a counter-sunk flat head screw, with a thin shaft and hex head protruding from the flat head. The hex head is used to drive the bolt into the countersunk hole, then the wrench or hammer is used to knock the shaft and hex head off of the flat head, leaving only a smooth screw head exposed. Removal is facilitated by drilling a small hole part way into the outer part of the head and using a punch and hammer at a sharp angle in a counter-clockwise direction. This type of screw is used primarily in prison door locks.