A few months back I picked up a pawn shop orphan mdl. 15-6, 4". I was told that it was an ex-Alabama prison system firearm and, based on the well used condition, I don't doubt it. The rear sight blade is chewed up on one side so I'd like to replace it.

I understand that the screw and nut will need to be replaced as well. My question is in regards to blade size. Numrich shows a .126 and .146 size. Is this the notch size width or height? Or is my assumption completely wrong and it's some other measurement.

Thanks in advance for your assistance!