PosiDrive screws were designed for automatic-feed screwdriving robots. You can tell them from a Philips by noticing that there are small lines eminating from the centre of the screw-head at a 45 degree angle from the main slots. Robertson screws don't work in automated-feed machines because the driver-bit can (at 45 degrees where the bit refuses to enter the hole) jam the machine. McFeely makes great screws...good steel and they stick to the driver nicely. The guy who invented the slotted screw should be forced to listen to Celine Dion.
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