The most common mistake people make when purchasing hose clamps is buying a clamp with the same INSIDE diameter as that of the hose. For example, if they purchase a 1-1/2 inch hose, they buy a 1-1/2 inch hose clamp and do not compensate for the thickness of the hose. Hose dimensions are always an INSIDEdiameter (I.D.).
Maximum diameter is always consistent on S.A.E. hose clamps. However minimum diameter varies by manufacturer +/- a few millimeters.