Outerwears pre-filter fits many stock and aftermarket airfilters on Gopeds and other scooters, pocketbikes, and R/C vehicles. Fits stock HPI Baja 5b filter. Fits unifilter, 3" K&N filter, and Carbon UFO filter snugly. Fits loosely on smaller filters (DDM filter, UFO filters, Stalker filters, etc). Does not fit shielded filters, or filters larger than 3" in diameter.