I'm now measuring the inside width to determine the nominal cross section thickness as compared to just the thru-hull from above. The inside width measured 24.16 millimeters. If you subtract 24.16mm from 35.33 you get 11.17 millimeters. That 11.7 millimeters then needs to be divided by 2 because I had to measure the OD/ID. To figure nominal wall thickness I used the thread depth of 1.26mm. Measuring these threads, inside the flange, would have been very hard and most likely not precise and they should theoretically be the same as the threads on the top of this fitting which I could measure.
So in summary outside width was 35.33 now subtract 24.16 and you have 11.17. Now divide that by 2 and you have 5.58mm now subtract the thread depth of 1.26mm (as measured from the NPT threads on top of this 3/4 fitting) and you get a nominal wall thickness of 4.32mm millimeters.
With a nominal wall thickness of 4.32 millimeters this flanged adapter plate, at its base, is more than 2.8 times the thickness of the 1" Apollo thru-hull fitting I measured above.