As I recall, there was an experimental frame size (the "C" frame?) that went nowhere. I do not think any of those test platforms survived, but it's not my knowledge set and I had never heard of them until someone who actually knew what he was saying discussed them here. My understanding is that it was between the J and K.
With that exception, which I mention only to be clear, the frame sizes in recent/current production are the J like your 36; the K (original hand ejector/M&P revolvers and their derivatives like the Combat Masterpiece, the Targets guns, and Combat Magnums); the L (just a bit bigger than the K: 586/686 etc); the N (357 Magnum/M27, .41 and 44 magnums, and the 45ACP and Colt revolvers), and the X (460 and 500). I did them in order of size, from smallest to largest. The "I" frames preceded the "J", and are just a bit smaller. At least some of the models originally made on the I are now on the J. This is NOT a complete listing, but just examples of the models in the various frame sizes.