Fit this over your Twin Air filter when your riding in severe conditions such as heavy dust and sand. This coarse foam pre-filter will act as an additional layer of protection. Extends the service time between filter cleanings. Designed for use with Twin Air filters. Fits: Yamaha WR/YZ400F 98-99, WR/YZ426F 00-02, WR250F 01-02, YZ125 97-13, YZ250 97-13, YZ250F 01-13, YZ450F 03-09.