#2, Stainless steel

US Fasteners

Sheet metal screw

Sheet metal screws

Screws with large threads for use in sheet metal sometimes also used in plastic, fiberglass, or wood.
Machine screw

Machine screws

Screws with machine threads for use with a nut or in a tapped hole.
Socket product

Socket screws

Screws with an allen wrench drive.
Set screw

Set screws

Screws with no head and machine threads for use in a tapped hole.
Nut

Nuts

Nuts have internal machine threads, for use with machine thread bolts and screws.