Inch Series (IS)
Inch Series (IS) fittings feature longer threads for compatibility with deeper valve ports.
Hamilton Valve (HV)
The Hamilton Valve (HV) fittings feature shorter threads for shallow ports.
IS or HV fittings should be selected based on the depth of the port. It is important that the fitting is long enough to extend all the way to the bottom of the port to ensure a leak-free seal. The nut length is included on the spec sheet for each tubing assembly.