This is a foregrip designed for the quad rail I designed for the shuty ap9. found here: https://www.thingiverse.com/thing:3081573 Will work on anything with a rail!
bolt size is 1/4-20. I used one from this kit from HF. It has a large locking nut so a standard 1/4-20 nut may be a little small.
update:9/22 fixed nut recess size
print as it shown with supports on print bed only and with a raft for best results.