You got me. The MR-42 had smaller everything in the HP section and of course the body. Cute little bugger isn't it?Even the MR-42? I just had one come in the shop and thought I had to order the special seat for the 42 (MR42 seat on left). Shaft looks longer.
New standard seat is on the right.
.View attachment 906515
And it's nice they still have parts available given the reg was only manufactured from 2006-2011 (as far as I can determine).
But I believe that's the only exception for the T shaped seats dating back to the days when AMF, which had acquired both Voit and Mares, decided to have Mares take over production of the Voit MR-12. The 12, 22, 32, 52, 62, 72, 82 and their XR counterpart diaphragm first stages all use the same size seat which first appeared in the double hose Aqua-Lung/US Divers Royal Aqua Master. (Or possibly the Aqua Master, but apparently the pin diameter changed during the AM production run.)