We have some information on common thread sizes (Inches and Metric).
The following illustrates the most common head styles for fasteners (screws to the rest of us).
The head styles shown above all show a slotted head type. This is entirely due to our modest (being polite) drawing/drafting capabilities. Almost all of the styles can be obtained in one or more of the head types illustrated below.
The flat and oval head styles shown above are both countersunk. That is, when fully tightened they are designed to lie flush with the surface (slightly protruding in the case of oval). Countersunk angles can vary widely with 90° being normal for metric and Imperial measures and 82° for UNC/UNF though as always multiple variants can, and do, exist.
Most head styles are available in a wide variety of metallic materials (steel, aluminum, brass, titanium etc.) as well as synthetic (non-ferrous) materials, such as, nylon (and other polyamides).
The following illustrates the most common head types for fasteners (tells you the type of screwdriver you need).
The head type Square above may also be known as Robertson after the inventor. (Thanks to Mark Snyder for the heads-up.) The Pozidrive (European) is subtly different from the Phillips head as anyone who has ever used a Pozidrive screwdriver on a Phillips screw can testify! (Thanks to Andy Lyke.)
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