But why have two different kinds of screws at all ... a socket screw invented by John Thompson that had a cross-slotted rather than slit head. To turn the screw, one had to use a tool that ...

It is very hard to apply lots of torque to a slotted screw drive without camming it out or snapping the head off the screw. The screwdriver isn’t self-centering either, so applying force off ...