Heavy duty reduction box twin-chain design for bigger torque transmission than standard reduction box with single chains. The reduction box comes with clutch(the bore on the clutch:1/2 inch=12.7mm) and 11/13/14/17/20 teeth total 5 pcs of sprockets.The sprocket fits T8F chain(8 pitch) only. Reduction Ratio: 3 to 1 chain reducer. Please confirm size of your original part. This is 91mm, not 116mm. Fit for 47/49cc 2-stroke Pocket Mini Bike / Scooter / ATV.