Hey All just a quick question I just picked up a 1995 15HP Johnson and the prop is a little nicked up but not bad was looking for props and all the charts say that it need;s a 9 1/2 x 10 but the prop thats on it is a 9 1/2 x 12 1/2 and its a stock prop.So whats the deal is that a special prop or what

Thanks

The first number in the prop size is the diameter. The second is the pitch of the prop.  To further decipher that,  think of a prop like a wood screw.  In the case of the prop you have already, with each revolution in the water, the prop would move forward 12 1/2 inches.  The prop you're suggested would move forward 10 inches.  In other words, the prop you currently have will provide more top end speed but less lower end power, the 10" one will be somewhat slower but will get your boat up on plane easier and faster.  

Thanks for the reply cart7  I understand how a prop work's just wondering   why this prop is a 9 1/2 x 12 1/2  when all the charts from Michigan wheel,solas,Turning Point call for a  9 1/2 x 10 the only thing I can find that says any different is at Discountprop.com

Its the only place that size is mentioned and it says it's mainly for 1993 motor's was it a speed prop?  

Prop sizes change depending on how many RPM's you are running.

I think most 2 stroke motors can run @6000 rpm max, and depending on how much weight you are pushing  will determine the prop you need.

The only thing standard when buying a prop...is the spline  and that is only standard for each of the same motors.

hope this helps

Dale