I have a whole drawer full of props, including several 11, 11.5, 12, 13, and 14 in a whole variety of pitches. I was just curious about that three bladed prop that came with the Evolution trainer engine. There are no numbers on it at all. In fact, the only marking on it is the Evolution trademark/logo. I was considering using a three blade prop to slow down my Midwest Aerobat w/ OS46ABX engine for a while until I get more used to it. It is rather fast with a standard 11x6 prop.