@Ricardus agreed, although I think the important geometry is the engagement surfaces more so than the overall external profile.
@elb Any bit that's conical in shape requires actual force to hold the bit into the fastener. Things like torx and Allen don't require that pressure for engagement.
@Ricardus That's true if the drive surfaces are an incline (like Philips) but not true if they are parallel (like pozi-driv or ... whatever that Japanese bit is that looks just like Philips but isn't). They're both conical in external profile, but the engagement surfaces meet at nearly a 90 degree angle, so they sit tight in their sockets.
Philips was literally _designed_ to torque out, and for some reason we use it for fasteners with moderate (though thankfully not usually high) torque loads.
@Ricardus See also hollow-ground flat blade screw drivers with parallel surfaces at the tip, versus your typical hardware-store flat blade with bevels.
@Ricardus That's what I'd call them, but I wasn't sure how widely-used that term is. In general, firearm screws have very high-quality cut heads with parallel sides, and hollow-ground fitted screwdrivers can turn them out with little to no chance of slippage.
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