letter K Leo Reynolds Flickr K Letter K Chris Flickr Letter K Floral Initial Free Stock Photo Public Domain Pictures K Letter K Chris Flickr. K&N XStream Top Universal Air Filters take performance to the next level with the addition of a filter within the filter's top adding more filter area for higher air flow and a longer service interval. The XStream Air Filter provides awesome air flow and outstanding filtration. When racing, in any environment, racers need all the protection and airflow they can get. K&N delivers. All K&N universal air filters are constructed with ultra strong molded pliable rubber flanges which absorb vibration and allow for secure attachment and can also be stretched for up to 1 16 inch (1. 5mm) to fit in between sizes. K&N universal air filters are washable and reusable.