I have been using this gun to spray adhesive for my restoration project.  https://www.yourautotrim.com/aespradspgun.html

Unfortunately, it fell off my work bench the other day (it is rather top heavy and I wasn't paying enough attention).  When it hit the floor the brass fitting that connects the gun to the cup broke.  Searching online, I haven't been able to find anything like this fitting.

I will try to determine the thread size today, but I know it is not pipe.  The nut on the right threads onto the brass fitting and can travel the full distance of threads.  It is a lock nut.  To secure the paint gun to the cup, the brass fitting slips through the nut on the left until the flat part at the bottom of the cone seats inside the nut.  Then the lock nut is threaded on.  Then the brass fitting is threaded down into the tube/cup portion of the gun.  Then you tighten and lock that nut.  The you tighten the large nut onto the gun and the gun seats against the brass cone. 

I hate to have to buy another gun because of this.  Let me know if you have ideas for a solution.
 

 

Can't you just solder the two pieces together?

A friction fit sleeve inside the tube?  And solder😄

I might have a donor gun?

Modify by hand? That is, put in a drill and use files to shape the cone end?
https://trumontsupply.com/products/12329_mm

Edited April 7, 2024Apr 7 by inline6

My sense is that the cone shape is less important (perhaps unimportant) than the ID of the delivery tube.  I suspect that the cone shape is provided to help prevent material from building up at the orifice exit.   A thin-wall brass tube sleeve (see GK's message, above) will certainly give more strength to a solder repair, but it may prove to be a matter of winning the battle while losing the war. 

My 2 cents:  Buy a new gun ($50).  Annoying, but pragmatic.