Please note that clamp sizes are approximate. Clamp measurement is not an exact science. Most manufacturer's specify that a clamp's measurement is across the smallest inside dimension with the clamp held in the closed position. If you are purchasing these clamps to hold wires or cables in position, exact size in not critical. We have had a few customers order clamps hoping to have them tighten perfectly over a certain size of tube. Unfortunately, we cannot guarantee this will always work out. Please let us know if you have any questions. Thank you!