I had a response from the nice man at SRM.
They sent me a different PRV with a letter explaining that they had tried several PRVs in various cases they have in the workshop.
They said that their PRV was made by CNC to the correct spec, and that they had discovered that theirs would screw into all the plunger cases OK, but was tight in all SA cases that they tried. They said that in their opinion, the tooling used by BSA had worn over the years so that the thread in the later BSA cases was slightly undersize.
Obviously the thing to do,- which I didnt, not knowing about this, is to run a Plug tap down the thread as Richard and others have done during a re-build.
The PRV they sent me is a few thou smaller, and I will try it when I can be arsed. They have offered to re-fund me if it doesnt fit which is good of them.
Also, new Stainless Steel PRVs to the std ball design are available at the moment.
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