Does anyone know the thread on the OEM Ruger SR22 threaded barrel? I have tried to find this information from Ruger support but they evade the question and reply that the thread is 1/2 -28. I know that is the thread on the male side of the adapter but I need to know what the actual thread on the barrel itself. I am suspecting it is some special tooling and if so why don't they just say so. I have duplicated the thread on a lathe and it looks like a  8.25-1.0 mm or 11/32 -28, neither of which or stand size threads and a tap is certainly not available is those sizes. What am I missing? Is it something obvious?
Thanks

Tag because I'm interested as well.

I tried measuring the factory barrel to see if I could use Twin Tech's Sparrow O-ring adapter but no joy.

If someone can post a top view picture of the barrel threads with a reference scale, we can figure out the thread size and pitch.

I asked around and the response I got was that the thread on the SR22 barrel is not a unified standard or metric standard thread.

It is a Unified Series 60° or ISO Series 60° thread.  It just may not be of nominal size.

 














 

Thread size is 11/32"-24 UNS-2A.

Major Diameter: 0.3427 - 0.3355
Pitch Diameter: 0.3156 - 0.3118
Minor Diameter: 0.2976 - 0.2848 (Ref)
Root Radius Max,0.0060

Ok Thanks!. I was close with the 11/32 but I was guessing a 28 tpi.. Still no luck finding that tap. Guess I will just give up on this project for a while.

You could always single point thread the internal thread.

For the female thread:

11/32"-24 UNS-2B

Minor Diameter: 0.299 - 0.308
Pitch: 0.3167 - 0.3216
Major: 0.3438 - 0.3547 (Ref)