These clamping angles appear to be well made and very accurate. In every way I could measure them, they are equal to 90 degrees. Of course within the tolerances of the tree. I used them to assemble a box with thru-hole joints (see photo). I like the box hinge pins that stick out a bit on the outside (they're easier to sand flush with the front of the box). So I couldn't place the squares on the outside of the box. You should have been inside. A small chamfer on the outer corner of the square for the adhesive gap would be nice. I glue the box joints so that very little (if any) glue oozes out, but I still think a bevel would be a good idea. It would also allow the two legs of the square to fit snugly against the sides of the box, even if there is some dirt left in the corner from cutting the box's joints. I'm not sure what the various slots and holes are for, but I assume they are for specific proprietary clips. I don't usually use special clamps; just old screw clamps. I was a bit concerned about placing the clip near the center of the groove. There isn't much material left on each side of the slot. For maximum accuracy, the clamp should be in the mid-third of the leg, which is not the ideal location for a slot. I had no problems with this project, but I didn't tighten the clamp either. Overall I think these squares are good value for money and are particularly useful for smaller projects where larger squares may not fit.