In article , raden
writes

For this particular screw head, I "concaved" it out with a drill bit,
then drilled the hole to take the nipple.

I then just cut 5 slots with a drivel pipe cutter

I'll follow your example, a good way to circumvent the ridiculous supply
restrictions the patent holder is trying to impose on the supply of tools for
these fasteners.
--
fred
Plusnet - I hope you like vanilla