Thanks for this, much cheaper than paying on the lathe.
Still looking for info on the rear diopter please. Does it help with sight alignment as the rear is slight different ID? I am at the point in life where bifocals are a necessity, hence my use of a non standard target as the black spot fits near perfect with a light white halo for sight alignment. When the black spot appears centered and the breathing is in the right point of cycle squeeze.
It helps with sight picture, the Centra basic diopter I have there is adjustable from 0.5-3.0mm so you can dial in the right amount of light and line all the circles up a little crisper then a fixed rear peep. Your fixed peep probably has a number stamped on it which is the iris size.
http://www.centra-visier.de/en/products/sights/iris-aperture/sight-30/