These clamps look like they were made in a Chinese foundry that typically makes mining or farming equipment. The tolerances are incredibly sloppy. No one bothered to check the shafts were spinning before shipping. With sufficient lubrication I got the shafts to rotate so that only a tenfold change in pressure is required as the various burrs pass through the bottom hole. On the other hand, they are heavy and hold up well. Luckily I don't have to adjust them much. It's frustrating when you have to switch between thin and thick materials on a regular basis.