V-slot rails end caps

End caps for the Openbuilds V-slot extruded rails.
Does not grab into the center hole, so it does not matter if you tapped a M5 thread in there..
Make these preferable in ABS, which is tougher and clamps better because it bends more than PLA

4 versions:
20x20 mm
20x40 mm
20x60 mm
20x80 mm