Replacement Backfire Air FilterTwin Air filters are slightly smaller than stock, making them easier to change while increasing dead air space around the filter for better performanceDual-bonded foam design filters out even the smallest dirt particles, while allowing more airflow than two separate layer filters (flow bench proven)Flat foam sealing ring provides a secure seat against the airbox, even in the worst riding conditionsIncludes a laminated layer of backfire-retardant foamReplacement filter for part # 1011-3960.