These Leybold oil mist exhaust filter replacement cartridge media are designed to fit into the Leybold AF8 oil mist filter body. It is important to replace your vacuum pump's exhaust filter media during each oil change procedure as part of a maintenance schedule. We recommend oil changes every 3 to 6 months. This is important because old oil mist filter media get clogged up with dirty vacuum pump oil. Did you know, that a clogged exhaust filter can damage your vacuum pump? The vacuum pump must exhaust the pumped air freely to atmospheric pressure. If the exhaust filter is clogged the exhausted gases will build in the oil casing during the roughing cycle. If the pressure builds high enough the pumps shaft seal, oil casing gaskets, or sight glass could burst causing a massive oil leak. This event would result in permanent vacuum pump damage requiring a vacuum pump rebuild service. These exhaust mist filter replacement cartridges are sold as 5 in pack.