The most common mistake people do when purchasing hose clamps, is buying the same diameter clamp as the INSIDE diameter of the hose. For example if a person buys a 1-1/2 inch hose then they buy a 1-1/2 inch hose clamp and don't compensate for the thickness of the hose. Hose dimensions are always an INSIDE diameter.
Maximum diameter is always consistent on S.A.E. hose clamps. However minimum diameter varies by manufacturer +/- a few millimeters.