As stated, John sent me an end cap off a Diana and it looks about the right size and thread, but I'm not very good at measuring internal threads at the best of time so there's scope for error. I don't actually know the manufacturers specification of the threads but I believe them to be M29 ? x 1 mm. The major dia of the external thread is 28.7 mm, and the major dia of the internal thread is 27.2 mm. My maths is rusty but to me that lines up more or less as the two threads being fairly similar, if not actually so. However, after looking at the Walther thread in better light than previous and after having cleaned it, I believe that it's damaged so my next task is to clean those threads up using a crude Die and check once more.

It's amazing how much thought from various individuals has gone into helping me sort my problem out (which I'm very appreciative of), but I might be flogging a dead horse as if when the Walther thread is cleaned up the Diana end cap doesn't fit I'm still back to the stage where an actual LP53 end cap is needed.

Vic Thompson.