Used to make frames on which I stretched the canvas. I checked several pieces of scrap to make sure the corners were straight. I accidentally put two 1" x 2" boards in the clamp, tightened the clamp and inserted a couple of pins to secure it, then measured. With a quick layout square I found a perfectly rectangular connection. The boards self-centered and came together exactly where I needed them. The clamps also have some weight and are slotted for attachment to a rework table.