Malossi Fly Clutch Bell for 50cc 4-Stroke 139QMB, Aprilia, Derbi, Vespas ScootersSPECIFICATIONS: Outer Diameter: 115mmInner Diameter: 107mmNumber of Splines: 22Fly Clutch is a reinforced centrifugal clutch designed to easily withstand extreme operation, for example, constant stop and go on steep roads, city traffic, long series of traffic lights, especially with a passenger, and during hot weather when it becomes difficult to control scooter temperature levels.Fly profits greatly from Malossi’s experience, results acquired from research and thousands of tests performed in the field of scooter racing.**