It was custom-made for the this drilling (my photo).
The gunsmith is a friend and will not make them for customers; the time involved to make and "regulate" each one to the rifle scares most people off. Also, there is quite a bit of empirical "fiddling" to get it right and he prefers things he can measure.
I can tell you the windage screws in the folding blade are 2/56, Allen-head, and the holes are hand-drilled with a small collet-held drill to prevent run-out. The post holding the blade is hand-filed after the it's threaded to match the original top-screw and a center line is determined (by a taught string from the front sight over the original rear blade then back over the post). After assembly, elevation is regulated by filing down a new front sight blade. Don't forget to put the original screw under the buttplate for the next guy.......
PM for more info.