The NAPA/WIX number for the ONAN B series is 1374, I use a 1762, it is actually for the CCK models, but its a taller version that specs out the same as far as micron, thread and gasket dimentions. The P218-220 series calls for a 1374 also, however the P224 calls for the 1762 cementing what I said above. The air filter number(s) are 2299 or 6094. The 6094 is the 2. inch high (low profile) and the 2299 is the 3. inch tall one. If you have any questions call me at Napa Auto Parts Grand Rapids MI. 616-363-4483 I keep them in stock for myself and a few other Case/Ingersoll folks here. Troy