Mushroom Head Screws

Mushroom Head: This has a dome head but is much larger in diamater to have a larger bearing surface

Phillips: 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 minimizes 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.