I received some questions as to the strength/robustness of the clamps we make. Long story short, these things take a beating.
First, some scrap rod was threaded into a cherry pair of clamps (with the counterbore).
Nothing could be done to damage the clamp in normal use, so the clamp was over-torqued with a pair of 12″ channel lock pliers.
The clamp was hooked over the edge of an I-beam and held my full weight (155 lbs). This skewed the jaws, but nothing failed and the clamp held its grip.
After continuing to over-torque the clamps, finally the body began to split.
The force to crack the jaw was so high the upper washer was embedded into the top of the jaw.
The final results were excellent. The threads never failed and the torque required to destroy a clamp was extremely high. (Sorry I don’t have actual numbers to put against this test, we’re planning to take some force measurements soon.)