Nitrah;

As has been stated it is most likely a BA thread.

When I retired and decided to continue in my hobby of restoring English side x side shotguns I decided that I need to learn to engrave. Screws needed to be engraved and actions needed engraving sometimes. So I spent 3 years learning to engrave.

I enjoy helping others like you who have a problem, so if will send the old screw down to me I will make you one, engrave and black it. The screw slot may or may not exactly line up exactly as one needs the gun in hand to make the screw that way. If you will pay the postage both ways I will make it for you gratis. PM me.

Kindest Regards;
Stephen Howell