simple version - just screw these into the board

modular version - screw the base on the board and put hex nuts into the slots on the underside, the size of the slots might need changing for other hex nut sizes

then you just need to screw the upper half of the rails using the nuts in the base, this makes it simpler to replace the rails after grinding them out or the rails cracking (i'm not sure about the strenght of the rails yet, but PETG (or stronger) is surely a better option then PLA

! higher temps for better layer adhesion