Oil filters are cylindrical pressure-drop filters positioned in the engine’s oil lubrication system. They remove ferrous particles, dirt, and combustion byproducts from circulating oil, protecting critical engine components from wear. Filter media typically consists of pleated cellulose, synthetic blends, or full synthetic materials, varying in efficiency measured by micron rating. Construction includes a metal housing, internal bypass valve to maintain oil flow during blockage, and a threaded mounting boss compatible with vehicle-specific adapters. Anti-drainback valves prevent oil from flowing back into the sump when the engine is off, ensuring immediate lubrication upon startup. Filter capacity is rated in quarts or liters and dictates service intervals.