I have a late BSA LJ (serial23xxx), and I have never been happy that the loading tap screw is correct. What I have is a motley assortment of washers, including a spring washer, held by a sort of combined screw and washer with a taper on the upper part of the shank. (I tried to post pictures, but as so often the technology defeated me).
I think what should be there is the knurled nut and spring shown as "no longer available" on the John Knibbs website, https://www.airgunspares.com/ljbp3rd...plugscrew.html. Can anyone confirm this please?

I now have a chance of someone making one for me, but I would need to know what the thread is so that I can buy a die. Any advice would be greatly appreciated.