99-08 HONDA TRX400EX: Outerwears Pre-Filter (K&N/Black) Founded over 33 years ago, Outerwears was created to fulfill a desperate need to keep the Air filter and engine clean during off road racing. They have been on the forefront of pre-filter technology by inventing and developing the water-repellent pre-filter for use in all types of vehicles. Outerwears has a product for virtually any air intake application. Water-repellent pre-filter combination prevents any water, dirt or sand particles down to 0.005" diameter from getting into your filter. Reduces filter and engine maintenance and wear.