Amazon.com: Flange Coupling Connector Motor Shaft Coupling D-Shaped Wheel Metal Shaft Coupler for Mecanum Wheel Motor Shaft Industrial Robot Parts : Everything Else
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6 mm D to Hex Adapter - AndyMark, Inc
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Shaft Sleeve 1/4Inch(6.35mm) Shaft Motor to 11mm Bore Adapter for RV030 Worm Gear Speed Reduce: Amazon.com: Industrial & Scientific
Amazon.com : SmallRig D Shaft D-Ring 1/4 Inch Male Mounting Screw Adapter for DSLR Camera Rig Quick Release Plate - 838 : Electronics
Potentiometer adapter from "D" shaft to full shaft. - Retroamplis
4mm to 6mm Shaft Adapter - Dia converter
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Pololu Aluminum Scooter Wheel Adapter for 6mm Shaft | POLOLU-2674 | Core Electronics Australia