[Spridgets] half shaft retainer

[derf]

OK, there is a difference.  But, I contend that you can use a Phillips
screwdriver on them.  Also, even if you do use the "correct" driver,
it will "invariably destroy the screw head" after 10-12 torquings, or
sooner if you apply too much torque.
You can certainly get more torque on a Posidrive, but the application
stated doesn't need so much torque.  I generally cheat on removal of
those things anyway and use a 3/8" impact wrench with the "proper"
tip.
I didn't want to start an argument on this but I don't want people to
think they have to go hunting for a special screwdriver if they just
want to do a brake job.  The two Posidrive screws just keep the seals
in place when you remove the wheel and brake drum and the one just
keeps the brake drum in place if you remove the wheel.  Once the lugs
are tightened the Posidrives aren't critical and aren't even useful
until you remove the wheel.
If you're a fastener snob then you'll want to replace them with Torx
drive screws anyway.  Do they make a 1/4-28 flat head TorX?  Isn't
that a 1/4-28 screw?
Cheers,
Derf