This post will be a visual aid for some of the different types of screws and bolts focusing on different heads, drive types, and bearing surfaces. The “bearing surface” or underside of the head, is where the fastener head makes contact with the device. To increase the tensile strength; some bolts, screws, are partially threaded with a shoulder below the head.
Here is a breakdown of the different types.
Bolts – are a type of fastener made with external threads that pass through a hole and fasten in place with a nut to a specific torque spec. The most common head type is Hex. Other head types Spade, Square, Carriage, T type, U Type, Eye, etc. Depending on the application, the thread type is either coarse(UNC) or fine(UNF).
Cap Screws - are similar to bolts, but with tighter tolerances. These also have external threads that fasten to the mating object. The Hex style is also known as “Hex Finished bolts”.
Machine Screws - Normally used for precision applications. It can either be used with a nut or threaded holes on the device. The threads are uniform diameter across the shank. They are affixed to the equipment by using a bit placed on the head, such as a Phillips, flat, hex, etc. is used to rotate the head and thread into the device. The thread size can be either fine or standard. The threads are either cold rolled with precision dies or the threads are machined into the shank.
Panel Screw - Has an unthreaded and threaded section below the head. The unthreaded section keeps the screw freely attached to the equipment panel.
Sheet Metal Screw - Is a self-tapping or self-threading fastener with a nonuniform thread.
Shoulder Screw - This is a fastener with an unthreaded section on the shank below the head. the smooth section makes it easy to use with a bearing, pully, gromet, etc.
Thumb Screw- Is a screw with a head that can be turned using the thumb and fingers.
Set Screw- Is a fully threaded screw with no head that is used to hold against or within another object.
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