Universal Filter Universal Clamp-On Air Filter 5in Flange/6-1/2in Base/4-3/8in Top/8in Height (KNNRU-2805XD)K&N XD air filters use a Deep Pile Design, Extra Fine Weave Grade Cotton and alternate geometries for added efficiency and capacity for off road conditions. This extra thick filtering medium provides the increased protection demanded by high dust conditions while continuing to provide the performance necessary to stay in the front of the pack. The XD Cotton medium was developed for the extreme conditions encountered by race teams in the Baja 1000.