This is a CNC mill clamp for my CNC 3040T mill. I use it with M6 hardware , The mostly i use is a M6x60mm bolt, so probably M6x50, M6x60 and M6x70 bolts fits all you needs for the 50mm Z height limit of these machines.
Designed from scratch but based on this thing shape:https://www.thingiverse.com/thing:21057
Print on .STL position.
I used ABS at 30% honeycomb infill.