Model originally uploaded to Thingiverse at https://www.thingiverse.com/thing:2196905.

This is a height adjustment foot, using an M8 bolt and M8 nut. There's a base plate which accepts an M8 nut and has four M3 mounting holes, and is designed to mount on a flat surface. The foot accepts an M8 bolt head and is in two parts, which can be glued together to enclose the bolt. The foot has a rounded hexagon shape, to make it easier to grip and turn.