John Henry Phillips, of Mass. patented his double slotted screw
in 1932. The very similar Reed-Prince screw is not approved for
aircraft, whereas the Phillips is. The Reed-Prince head is an
imitation Phillips that is designed to eject the screwdriver
when pressure is sufficient to break the head of the screw. Inside
the slots of the Phillips are some multiple ramp angles that
will cause the screw driver to lift out before you can break
off the screw head. The Phillips greatly increased production
because the screw could be balanced on the screw driver prior
to insertion.