I drilled and tapped for, and used, 6-48 screws. Had to turn heads down a bit to fit in sight base counterbores. The original Lyman screws mic at the same as 6-48, and the thread gauge confirms it, but, those screws in turn would not go in the whole way without forcing them. I wonder if Lyman supplied screws with an interference fit to prevent loosening? Like I said, I didn't want to force anything so I went with new ones for my recent Lyman 54 project.
