This is an APC 18x10 Electric Propeller. FEATURES: Composite propeller construction Thin propeller ONLY designed for Electric use INCLUDES: One propeller SPECS: Center hole diameter: 1/4" Propeller diameter: 18" Propeller pitch 10 COMMENTS: The propeller comes with five locating rings: .128 .158 .197 .237 .313 the locating ring combines with the hub to create a precision fit. ajw 7-11-03