This is a 5.1x4.5 Thin Composite Electric Propeller from APC For use on Electric powered aircraft only (not for glow engines). FEATURES: Gray composite propeller blades that assemble onto a propeller hub. Comes with two adapter rings that adapt to different motor shafts. INCLUDES: One composite propeller Two composite adapter rings One instruction sheet REQUIRES: Assembly onto motor or gear drive unit in your Electric plane. Balancing SPECS: Diameter: 5.1" Pitch: 4.5 Hub inner diameter: 0.25" kpm12/20/2006 ir/jxs