ShapeOko Clamp Set

Same dimensions as the original one (https://www.inventables.com/technologies/clamp-set).

Just put a M5 nut inside and block with the small piece.
Screw with a M5 screw on your table (adapted with this http://www.thingiverse.com/thing:414443) and use a second M5 screw flipped in order to maintain at the right height.
This allows you to adjust the clamp so that is less likely to damage softer materials.
Use the nut if you want to tighten with your fingers.