GOOFIT 58mm Air Filter for 2 Stroke 37cc 39cc Water Cooled Pocket Bike Mini Bike MTA4 The item fits for 2 stroke 37cc 39cc Water-cooled Engine The flange diameter of the air filter:58mm Engine opening diameter:20mm Arrival within 1-2 days (Sold by GOOFIT and Fulfilled by Amazon) Arrival within 7-15 days (Ships from and sold by GOOFIT)