The 3/8" OD of this servo shaft allows you to slide a 3/8" clamping shaft coupler on and clamp down to create a servo to shaft coupler. The other side of the clamping shaft coupler can be any size you wish to use so that you can attach the shaft diameter of your choice to a servo.
The combination of the clamping coupler and this servo shaft will make one of the most solid and versitile servo to shaft couplers available. Patented.
