Flexible Couplings 5mm to 8mm Compatible with NEMA 17 Stepper Motors * Compatible with NEMA 17 stepper motors (for 5mm shaft diameter). * Flexible Couplings made of premium aluminum alloy material, exquisite workmanship, bright appearance, good toughness. * Flexible coupling can eliminate the stress between the motor and drive parts. * Coupler diameter 19mm x height 25mm.0