Soup Nazi wrote:
which screw head is better? for a non-slip power driver's use. And what
type for shear-resistance? outdoor/indoor etc?



I believe the Roberts (square drive recess) is better in many ways. It
stays on the driver "no hands" pretty well without needing magnetism.

The recesses "strip out" less frequently than Phillips do, which means
the bits will last longer, 'cause they wear when they spin in the screw
head recess.

The Pozidrive recess is a good compromise, Screws can be reliably driven
in initial assembly with the correct bit, but they can be removed for
servicing by anyone with a plain Phillips screwdriver.

McFeelys has a lot to say about square drive screws.

http://www.mcfeelys.com/

HTH,

Jeff

--
Jeffry Wisnia
(W1BSV + Brass Rat '57 EE)
"Rudeness is the weak man's imitation of strength."