G-
All measurements is inches
ID=1.875 OD=1.900 H=0.500 This with a steel backing that is OD=1.749 ID=1.652 H=.425
AND as the previous post states, there are 4N & 4S.
The spindle the mag/backing plate bolts to tapers from a 1.25 to a 1.30.
Knowing this there is certainly room for smaller backing and larger (thicker mags.).
Will be good to "play" with.
Bruce S