Do you need to restrict/reduce the speed of your scooter for legal or insurance reasons then this simple method using a limiter ring is a great option. These rings fit all scooter variator axis with an external diameter of 20mm including 50cc Piaggio scooters, 4 stroke Chinese scooters with engines 139QMA/B or Kymco and SYM 50cc scooters. All rings are 20 mm inner diameter, of the outer 25mm. Variator ring dimensions: (ID x OD x Thickness): 20x25x6mm