9.5 3/8" x 10mm Flexible Shaft Coupling Stepper Motor Coupler D25 L30: Amazon.com: Industrial & Scientific
Aluminum Flex Shaft Coupler - 5mm to 8mm : ID 1176 : $4.95 : Adafruit Industries, Unique & fun DIY electronics and kits
Amazon.com: Sydien 2Pcs 5mm to 10mm Motor Shaft Coupling Aluminum Alloy Flexible Stepper Motor Coupler Motor Connector Joint for 3D Printer, CNC Machine : Industrial & Scientific
Shaft Sleeve 1/4Inch(6.35mm) Shaft Motor to 11mm Bore Adapter for RV030 Worm Gear Speed Reduce: Amazon.com: Industrial & Scientific
Custom OEM High Strength Motor Long Shaft Adapter CNC Stainless Steel Motor Shaft - China Motor Accessories and Machinery Part