Socket screws have an allen wrench drive.
Flat heads are countersunk (cone shaped under the head) with a flat top. Allen (hex socket) drive is a six-sided recess for use with an Allen wrench (hex key).
A high strength heat treated alloy steel. A heat-treated alloy steel for applications where very high strength and hardness are required. A chemically produced coating that leaves the steel surface with a matte black finish and offers mild corrosion resistance.
Screws with no head and machine threads for use in a tapped hole.
Screws with an unthreaded shoulder that is larger in diameter than the threads. Also known as stripper bolts.