25 Series 16 Tooth 6 mm Bore Aluminum Sprocket

Works great and doesn't require a special d bore sprocket.

'This split sleeved sprocket and clamping collar design is well worth the price to gain the very highest level of sprocket to shaft torque transfers needed with FTC 6mm shafted motors. Grip has been maintained at high level even during frequently reversing loading and impact loading with no slippage.
The $20 price pays off big time in reliability benefits. Forget the set screw concept for hub-to-shaft higher torque transfer duty; performance of this design totally kills that concept.'