Threads for caps

[MMH]

The 300 WM suppressor that I am designing is going to have threaded caps on both ends. I am having trouble figuring out the thread details. I don't expect that there are standard extra fine ptch threads for a 2" tube. What is a decent TPI and where do I get the thread profile details?

[fishman]

24 28 and 32 are popular

heres a diagram of ISO standards

[T-Rex]

Not going against what Fishman said, I've always done this: (specifically for a tube plug, aka end cap)
(ID+.01)+2(.868*(Insert Pitch))= Major Dia. (add your own tolerances here)

I add the .01, to the ID, so the female threads have additional clearance (.005 per side), for when you slide baffles in and out.

[BinaryAndy]

As fishman said, 24, 28 and 32 TPI threads are common. Around 0.75 to 1.0 mm pitch would be good if you're into that sort of thing. You're right, there won't be a standard size that works right. Just pick a pitch, and make the minor diameter the same or a few thousandths larger than your tube's ID.

Here's a handy thread calculator thing that will give you all the important information about your wacky custom thread sizes: http://theoreticalmachinist.com/Threads ... erial.aspx

[propeine]

Not going against what Fishman said, I've always done this: (specifically for a tube plug, aka end cap)
(ID+.01)+2(.868*(Insert Pitch))= Major Dia. (add your own tolerances here)

I add the .01, to the ID, so the female threads have additional clearance (.005 per side), for when you slide baffles in and out.

That's pretty much what I do as well. Major Diam = measured inside diam + (2 * 1/TPI * .866) - .002. Then keep making passes until it fits, lapping compound to finish.

I generally run 24TPI for end caps. Just under half the tube thickness for everything I've done with sharp V threads.

[daviscustom]

I generally choose a pitch that leaves enough material on the tube around the threads so that you are still comfortable with the strength....I like to leave as much meat as possible. The can I am working on now uses 40 tpi on a 1.75" tube. Other then tube strength concerns, it is whatever floats your boat on the pitch you choose. 40 tpi is low profile but your wrists get really tired if you have take your caps on and off a lot in one sitting....lapping the threads was pretty brutal

[MMH]

Thanks for all the replies!