Allows you to use a plain M4 nut in place of the more expensive T-Slot nuts. I don't recommend using these for the main structural components of a MendelMax until further testing is done, though they would probably be fine, but they will be perfect for adding accessories. Print them out, clean up the hole if necessary, insert an M4 nut. FAQ: Q: Why m4? Why not use M5? A: M5 will not fit in the slot. An M5 Jam nut might fit, but I have not been able to source them locally.Q: Can I use a 6-32 nuts? A: Probably. I have not tested 6-32 nuts, but they should fit, with some minor adjustments to the CAD file. I will pick up some 6-32 nuts and confirm.