BQLZR Golden 2mm x 2mm Brass Joint RC Aircraft Motor Shaft Coupling Adapter Connector Pack of 2 Ideal accessories for RC Model motor, such as airplane boat model. Widely used in metal, mold, mechanical drive applications. Between the transmission member can do both screw can do model remote control boat propeller shaft and the motor power. Connecting two axis with different diameters, can also be connected with a motor axis, or connecting shafts of different diameters. Diameter: 9 mm