Dave,
I was a little perplexed at your last reply so I looked at my SBT. I looked for the pin/screw with the naked eye and didn't see it. Only after I got a magnifying glass was I able to detect the round circle indicating that the pin/screw was there. The matting and the blueing was perfect. I always assumed that the rib was held on the breech with solder. How can the screw work it's way loose when the matting on the pin head lines up perfectly with the rest of the matting on the rib?
How do you know the dimensions of the screw? Did you take it out? Inquiring minds want to know