The oil filter helps remove contaminants from your car engines oil that can accumulate over time as the oil keeps your engine clean.The outside of the filter is a metal can with a sealing gasket that allows it to be tightly held against the engines mating surface. The base plate of the can holds the gasket and is perforated with holes around the area just inside the gasket. A central hole is threaded to mate with the oil filter assembly on the engine block. Inside the can is the filter material, most frequently made from synthetic fiber. The engines oil pump moves the oil directly to the filter, where it enters from the holes in the perimeter of the base plate. The dirty oil is passed (pushed under pressure) through the filter media and back through the central hole, where it re-enters the engine.