see thread belowI have posted on a few forums about reverse engineering the 98A sight.
I have a complete set of drawings and have actually made a couple of sights, one of which I have on my early 1936 model 71.
I will send you the info on the screw if you PM me your email address.
The screw is a modified 4-40 and the nut is made by drilling and tapping a screw head.
The modification to the screw is to center drill the end of the threaded section, 0.030 dia by 0.020 deep.
This mod is necessary for the flaring of the screw end after the nut is installed to keep the nut from coming off.
The screw is in fact used to adjust the windage. If it was screwed down too tight, it will not function. The sight base has half the screw hole and the windage piece has the other half. The sight base is threaded, but the windage piece is not. It's not threaded so that the screw can allow the windage piece to move.