Hey, I'm mtf, still early transition, and I have always had small fingers. I wear a 6.75 to 7 on my ring finger. The largest ring size I can wear is a 9 but that's on my index finger! Every time I wanted a ring pre-transition, I had to have it sized and usually they couldn't make it small enough and it still slipped off. There are plenty of guys that have trouble getting a "men's" size ring.
~Kristen