Yah, sybrmike
That stud is a through stud that is machined to the inside of the hole in the arm. When you tighten the nut on the outside it pulls against the rudder shaft to help keep it in place? Good thing I didn't beat on it too much!! LOL I have a bunch of weird pullers from a former life and it came off without any fuss once I got one on it with a good fit.
I'm new to boat repair and even when its all apart it doesn't make any sense