[JRTJH]

I can't tell you what the exact differences between pneumatic and propane QD fittings, but I'd make a guess that it's the machined tolerances. Most pneumatic fittings have a statement on the package that reads, "Not for use with flammable gasses"..... There have been a number of posts on this forum and on other forums stating not to use the air compressor fittings on any propane QD hose or outlet.