The K&N RU-5138 is a round tapered universal clamp-on air filter with a 6-inch centered flange, a 7-1/2-inch base, a 4-1/2-inch top, and a 5-inch height. It uses K&N's oiled cotton gauze media and is built for custom induction tubes and aftermarket intake builds, not one specific vehicle airbox. The manufacturer's universal line describes a flexible rubber flange that absorbs vibration and can stretch about 1/16 inch to bridge between sizes, which helps it seal to a 6-inch intake that is close to spec. Because the filter is washable and reusable, a buyer who runs K&N over a disposable paper element can clean and re-oil it instead of rebuying every service interval. The manufacturer's universal filters list cleaning intervals of 75,000 highway miles or five years at 15,000 miles per year. For a clamp-on performance intake, correct flange diameter matters more than brand, so confirm the 6-inch inside diameter against your tube before ordering. Long-tail searches: 6 inch flange universal clamp-on air filter, round tapered cotton gauze air filter, RU-5138 K&N 6 in flange, custom intake washable air filter.
The manufacturer states that the molded rubber flanges on its universal filters can be stretched up to 1/16 of an inch (1.5 mm) to fit in-between sizes. This is a small margin, so the intake should be close to 6 inches before you rely on it.
Yes. The manufacturer describes K&N universal filters as washable and reusable. Its universal line lists cleaning about every 75,000 miles under normal highway driving, or about every five years at 15,000 miles per year.
This is a clamp-on swap rather than a bolt-in part, so the work depends on your intake. Per the manufacturer's install guidance, the filter slides onto the filter adapter or intake tube and is secured with a hose clamp. Some K&N filters go into the air box lid first, so hold the element in place with your fingers while you refit the lid. Make sure the filter seats in the lid groove and the lid sits on the base before fastening the clips. K&N filters usually need more clamp pressure than an OEM foam seal, so if the clips feel excessive or the air box flexes, stop and recheck the fit to avoid cracking the housing.
