Imperfect design. Not recommended for thin, low profile clamp projects. Will not clamp to less than 3/8" thickness. The clamp just springs on its own. The clamp works great with material thicker than 3/8". I machined 10mm Delrin washers and epoxy bonded them on the tips to solve this problem.The spacers ensure that the clamping geometry works correctly.The spacers also protect the workpiece from scratches caused by the rough surface on the tips of the clamps.