First off, the rule when converting from 2-bladed to 3-bladed props is reduce diameter by 1 and increase pitch by 1. Example, I have an 11x7 prop on my 2-stroke .61 engine I'd then use a 10x8 3-blade for this set-up. Master Airscrew has a complete line of 3-blade props in conventional and pusher orientations. They are a bit pricey as you move to the larger diameter end of the spectrum. Also, Dubro offers an array of 3-blade compatible spinners to accompany the prop. Nothing like good 'ole experimentation to determine whether the move to 3-blade offers any improvement in thrust. Good luck!