Hi, I'm not an engineer so I'm sorry if this seems like a dumb question, but I'm designing a part that is a piece of 1.5" titanium tubing that is threaded on the inside so that a cap can be screwed on, similar to the cap on a Mag Lite.
Can a tube a wall thickness of .039" be used for that?
What should the thread pitch be?
It all depends on the thread pitch, but as you asked what pitch you should use you're on the right track. 16 TPI for example would not work as the depth of the thread is .0338" and that wouldn't leave too much meat on the wall. I would go with 32 TPI whose thread depth is .0169". Are you going to thread this with a tap or use a lathe? Finding a tap like that would probably be very expensive. If doing this with a lathe you better get or make the male part first as it's probably smaller and cheaper to make than the tube part as you'll need to continually test as your cutting to make it fits correctly before taking the part off the lathe.