These replacement filter elements fit on the VR1000 vacuum regulators used on traditional AirSep systems between 1994 and 2004/5. Note: This element will not work on pre-1994 vacuum limiters, which can be identified by their metal, gloss black body. The vacuum regulator controls the maximum vacuum level attainable in the engine crankcase should the main air filter element get dirty or fouled with exhaust soot.