Unlimited size very strong C-Clamp Adjustable

A adjustable clamp. The clamp jaws slide along a 20x20mm alu profile and can be fixed in place by thumb-screws. Additionally each side has two 4mm holes to screw with t-nuts into the alu profile. This helps to stop the clamps jaws from sliding along the profile at high clamping forces.

The clamp width just depends on the length of the aluminium extrusion profile. In principal any 20x20mm sqare stock will work. But you might only be able to fix the clamp sides with the thumb screws.
 

By only fixing the jaws with the thumb screws to the profile I achieved about 20kg (44lbs) of clamping force which should be enough for most use cases. With the additional M4 screw that hold with t nuts directly in the profile I did achieve 55kg (120 lbs) without noticeable deformation and without damage. I have not tested the clamp till failure jet.

To assemble the clamp just screw in the clamp screw into one of the clamp sides and then screw on the anti rotation pad. When the pad is crewed on all the way in it drops free from the thread and allows for free rotation to counteract the rotation of the screw. Next screw in the fixed pad to the other clamp side. Now slide the two clamp sides on the alu profile and fix them in place with the thumb screws.