GOOFIT 39mm Piston Kit Assembly for 50cc Horizontal Engine ATV Dirt Bike Go Kart The item fits for 4 stroke 49cc 50cc horizontal engine,not for GY6 engine or vertical engine The piston diameter:39mm The piston pin diameter:13mm; The length of piston pin:31mm Arrival within 1-2 days (Sold by GOOFIT and Fulfilled by Amazon) Arrival within 7-15 days (Ships from and sold by GOOFIT)