Clippard bulkhead fittings come with the internal thread of 10 - 32, 1/8 NPT and 1/4 NPT, Thd Mtg. of 15 / 32 - 32, 1/8-27 NPT and 3/4-20.
Other specifications include "A" (0.500", 1.000" and 1.000"), "B" ( 0.125", 0.250" and 0.250") and "H" hex (9/16", 7/8" and 7/8").