I have 1.5" shafts A22. From what I've been hearing that is in the middle of the safety range for sizing, but please correct me if I am wrong. I figure that with the torque of the diesels I should be able to swing the biggest props my boat can swing, but with safety in mind. That's what I am trying to do...fit the shaft to the prop to gear to the engine...in no particular order, before I make more moves on this conversion.