This servo to shaft coupler is intended to fasten a 1/4″ shaft to the output spline of a servo that has a 25 Tooth (3F/H25T) Spline. The coupler fastens to the servo by installing the stock servo screw down through the center of the part prior to inserting a 1/4″ shaft into the bore. For a solid connection between the coupler and a shaft, we recommend that you use a 1/4″ D-shaft so that the set-screw is able to tighten down on the flat and reduce any chance slippage. For round profile shafts we do offer a similar coupler that clamps around the shaft rather than using a set-screw. Patented.