This is a 11x8 Electric Pusher Propeller from Advanced Precision Composites. For use on electric powered aircraft only, not for glow powered engines.FEATURES: Constructed of Gray composite material Five adapter rings that adapt to different motor shafts INCLUDES: 11x8EP Thin Electric Pusher Propeller, two adapter rings and instruction sheet REQUIRES: Assembly onto motor shaft or gear drive unit in electric planeSPECS: Diameter: 11" Pitch: 8 Hub inner diameter: 0.375" (9.5mm) where rings are installed Inner Diameter of Rings: 0.128" (3.25mm), 0.158" (4mm), 0.197" 0.237" (6mm) and 0.313" (7.95mm)