Measurement is equal to OD of cover gasket. This QMB139 (GY6-50) scooter transmission belt and clutch cover is for the long case motors.
Common applications include:
E-Ton 50cc Sport (ESport) (Vin: TCA)
Ice Bear MADDOG PMZ50-19 50
Ice Bear MOJO PST50-8 50
TaoTao Racer 50
TaoTao THUNDER 50
Tomos NITRO 50