Captive screws lock in place, either with locking heads, clips that hold the screw in place, or a female sleeve that attaches the screw to a work piece. They are commonly used in the aerospace and computer industries, as well as other rapid assembly applications, and in environments where it would be dangerous for a screw to fall and clog machinery.
Concrete screws are designed with hardened threads that are not too brittle and can screw into concrete, brick and other hard materials.
Machine screws are driven into tapped or pre-drilled holes. Often used with nuts, machine screws are primarily available in smaller sizes and have blunt ends. They are often used to fasten metal parts together. Machine screws come in a wide variety of head and drive styles, but they are most commonly used with slotted or Phillips drivers.
Panel screws are designed to remain firmly fixed. They often mount flush with the object on which they’re used. To hold them captive use a retaining washer (sold separately). They have blunt ends and are used with computer parts, panel assemblies, cabinets, and other items produced on assembly lines.
Self-tapping screws have sharp threads that create their own hole when they are driven. They have sharp, pointed tips and are self-starting in soft metal, but require a pre-drilled hole with harder material.
Set screws generally do not have external heads. They can have blunt or pointed ends and are used for holding pulleys, gears, and other parts from turning relative to a shaft and to prevent loosening due to vibration.
Shoulder screws, also known as shoulder bolts, have threading only part way up the screw and then a smooth shaft close to the head to act as a spacer or bearing. The shaft is generally longer than the thread of the screw, and the point is blunt. Shoulder screws with round shafts are commonly used for items that require rotation, while those with square shafts are used to lock into place and prevent rotation. They are often used in mechanical or automotive applications. The length indicated for a shoulder screw denotes the length of the shoulder not including the head height or threaded length.
Socket cap screws, also known as Allen head screws, have a recessed drive, and are commonly used when there is not enough clearance for a conventional wrench or socket. They are fastened with an Allen wrench, which is also called a hex wrench or hex key.
Thumb screws are designed to be twisted into a pre-drilled and tapped hole by hand. They have blunt ends and are often used on electronics and computers.
Wood screws have coarse threads that are designed to help them bite into wood and resist pull-out. They have sharp, pointed tips that are designed for use in wood.