Good information. Thanks. So, the ideal would be a PT screw with a Torx head.
Or, better, yet, all boards use double holes on each end of the footstraps. My old formula boards use these, but my newer foil boards use singles. Hate those.
Swindy, no stainless in the larger sizes. I went through all their stuff online .....
segler I reckon you have been a bit lucky as the reason all the major brands went to PT / thread forming screw long ago is the Chinook self tappers ripped out often when jumping. I have used the same ones as you, but only had success with double screws each end and in brand-new Chinook inserts )which have a hole about 0.25mm smaller than the more common / standard inserts used by everyone else).
The annoying thing is the screw seems to be specially ordered by Cobra and Unifiber and then they sell individually at an obscene markup
Try these guys: screwerks
us.screwerk.com/en/products/stp.html
They don't have them in A4/316 but they have them in A2/18-8
So, yes, inspired by this discussion, I ordered some Screwerk STS-plus KN6038 6x25 - T30, stainless A2 - 1.4567, bright pickled and passivated.
These are perfect. Since we may already have torx T30 tools for our foils, we can use them with these screws. The 6mm outer diameter, and 25mm length is just right for footstraps in plastic inserts.