The shaft threads are different on mine. I mounted the new one in my Gieseke Nobler and the Tru Turn spinner adapter would not fit. I got the old one out and voila...like a glove. Not sure what the threads are on the new one but not the same as the old...That's the only difference I can find but have not done any measuring on anything...does run good though. Turns the same prop as the old one at same RPM, and yes it is broken in.