This APC Speed 400 propeller is sized at 4.1 x 4.1 inches, indicating a 4.1-inch diameter with a 4.1-inch pitch, designed for use with Speed 400 class electric motors commonly found in small RC aircraft. The set includes the propeller and a separate adapter hub assembly to fit the prop to the motor shaft. APC propellers are a widely trusted choice among electric RC fliers for consistent balance and performance. Features: 4.1 inch diameter, 4.1 inch pitch Designed for Speed 400 class electric motors Includes adapter hub assembly Two-blade propeller design 7/7/26 cs