Imperial CSK Phillips Screws

Counter sunk Head: This has a flat top and a tapered underside that is intended to be driven into a countersunk hole.

The Phillips head is an improvement to the slotted screw; cross-shaped grooves that do not extend to the edge of the screw head accept a Phillips-head screwdriver. These heads, which have a slight circular shape where the slots cross, provide a larger mating surface between the screw and the screwdriver, which minimises wear and helps prevent slipping. 

Machine screws have finer threads than wood screws. They are designed to be used in conjunction with a nut or tapped hole.