Briggs & Stratton Round Air Filter Cartridge - 394018S. This pleated-paper filter provides the first line of defense against the destructive effects of dirt ingestion. It is used on most 12.5 HP through 21 Gross HP horizontal crankshaft L-Head twin cylinder, and most Vanguardâ„¢ OHV V-Twin engines. This filter fits model numbers: 303400, 303700, 304400, 350400, 350700, 351400, 351700, 354400, and 384400. The pre-cleaner (272490S) designed for this filter is sold separately. The 394018s is the replacement for slightly larger 394018. NOTE: It is NOT meant for engine model series: 380400, 380700, 381400, or 381700. For these engine models, use air filter 692519.