This is a Master Airscrew 13x8.5 Nylon Prop for Electric Motors. FEATURES: Designed exclusively for Electric flight. Made of "glass-filled nylon for durability. Blades are wide and thin to provide the flex needed for hard landings Undercambered blades give great thrust and pull for superior perfor- mance. Bore size is a uniform 1/4" Use this 13x8.5 prop for geared 550 and 600 motors. INCLUDES: One 13x8.5 Nylon Propeller for Electric Motors. SPECS: Center Hole Diameter: 1/4" Propeller Diameter: 13" Propeller Pitch: 8.5" COMMENTS: These props are only for Electric motors. sdw 4/2/02 ir/kh