This K&N air box for Karts accepts one of two K&N washable/reusable High-Flow Air Filters. K&N filter RU-5006 features a 20 degree angled flange that is 1.5 inches in length and the RU-5005 offers a straight flange that is 1.5 inches in length. Air filters are sold separately. Either filter will snap into the RK-1000 Kart Airbox, then, the whole assembly clamps on to the carburetor. Many organizations that sanction Kart racing require air boxes like the RK-1000 due to noise restrictions.