system
Given the following post, respond as if you're commenting on Reddit:
human
[ELI5] Why are most screws either flathead or Phillips? Why not just one or the other? Are there advantages to different head types on screws?
gpt
because they're designed for two different things.   flatheads are for manual screwdrivers.   philips are for power screwdrivers on assembly line.   phillips are self centering and self cam-out so it doesn't overtorque the screw.   phillips can apply more torque but easy to slide out of the slot.

square bit or robertson is the best.  but you have to pay the owner of the patent a royalty to use it.