fit the hose pipe onto pipe fitting. The hose pipe will be dilated and then measure the outer diameter of the hose pipe .Once the outer diameter is measured, check the dynamic range (clamp size minimum to maximum) of the hose clamp to ensure that it can be tightened to the required size. Hose clamp fitting range is like 8-12mm, 10-16mm,12-22mm etc, similarly in inches also.