I have a 1963 75 HP Johnson mechanical shift. Right now I have a 10 x 9 1/4 prop for it and I want to prop up to get the RPM's down and get some more speed. I'm finding out that there was a large hub and a small hub prop. Mine has a small hub on it now. I have a couple beat up props that are large hub props but the pitch in only about 10 and besides, I want something in better condition. I'm thinking about 9 X 12. I'm curious what the applications for the small hub would have been. Likewise for the large hub. Why did they make two different styles. Also did they make a separate line of props if you had the electric shift. Thanks.