Round heads are domed and look like half of a sphere. Slotted drive has a simple slot for a flat bladed screw driver.
A corrosion resistant steel alloy. The most common stainless steel for general hardware use.
A low carbon steel for general use. Zinc plated for moderate corrosion resistance.
Screws with machine threads for use with a nut or in a tapped hole.
Screws with an Allen wrench drive.