A template to make gridfinity compatible pocket holes. The pockets are 84 mm apart, but you can use the indents to mark lines and reacommodate the template to machine at 42mmm spacing.
As it is, it's meant to be used with a 6mm bit and 17mm guide bushings(5.5mm offset).
I'm sharin the Fusion360 design too, it's parametrized so you can easily change the tools parameters.

Gridfinity needs 2.5mm depth pockets, but 3mm or a little bit more work fine :)

It's 9mm in height, so printing in 0.2mm or 0.5mm layer height will work great. And make a good bed leveling :)