I have an external mix single action brush from a package deal i bought.
The stainless steel (?) connector for the airline has threads for the air line
end however it has a smooth slip in end for the air brush body.... The
smooth slip end keeps popping out when under pressure.. My compressor
is set at 30psi, and ive rigged an adjustable pressure reducer but still
get the pop off.. would like to try to fix it... ideas are superglue (as a last
resort), a thin metal sleeve or duct tape sleeve to secure the seal.?
I can kind of hold the whole thing together using both hands but only
leaves my toes to adjust, hold the model.. ideas? help? Thanks

Could this piece be super glued or epoxi glued into place?

Maybe try a small hose clamp?

Try a product called Goop it has great holding power. Another thought would be a plastic tie the type the police use in mass arrests..not sure of the real name.

you mean zip ties? you can pick them up anywere and one should do I'd also think about a hose pipe clamp 9like the ones you use to tighten up your garden hose to the taps these also come in small sizes and having the extra width might offer a tighter seal than zip ties alone I'd use zip ties if you decide to go down that route

The stainless steel nipple slides into the hard plastic body of the brush.. apparently
it is supposed to just seal into the brush body by pushing it in.. so hose clamps are
out.. i tried a sleeve of duct tape which worked for one session.. ill try and get a metal
insert sleeve at the hardware store and see if that works.. if not ill try the goop stuff..
glueing is the last resort ( im afraid ill glue up the actual air hole).. thanks for the
assistance.

Well, if duct tape worked once, you might also try some teflon thread sealing tape, the stuff used on pipe threads. It would at least allow you to take it apart when needed. Good luck, hope you can work it out.