These are 3d printed workholding clamps for a CNC Router. They are intended to work with m5 and 1/4 20 hardware. The clamps trap a 1/4 20 nut and then a 1/4 20 bolt threads through it to form the foot of the clamp. You can use the "Bolt foot" part to give the head of the 1/4 bolt more surface area while protecting the surface of the bed of your machine. The m5 hand knob fits over the hex head of an m5 bolt, making it easier to turn and clamp your part down.

These provide plenty of clamping force for milling most materials, including wood, plastics and even aluminum. Also, if your bit comes into contact with the clamp, there's a good chance that the bit will cut through the clamp instead of breaking.