Suppressor thread question

[longshot]

The three suppressors that won’t fit on the new barrel can all fit on any of the other three barrels that are threaded 1/2x20.
The one that does fit the new barrel also fits on any of the existing three barrels. Only problem is it is a rimfire suppressor. (Cheap one that works and is probably cut to have plenty of tolerance like a.303 chamber)
The thread protector that fits on the new barrel fits on the three existing barrels too.

Judging by all of the above, the threads on the new barrel are just a touch too wide to go into a DPT