Socket screws have an allen wrench drive.
Socket caps have a small cylindrical head with tall vertical sides. Allen (hex socket) drive is a six-sided recess for use with an Allen wrench (hex key).
A low carbon steel for general use. Chrome plated and polished for a mirror like finish.
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.