Sealing and leak prevention: Designed with rubber seals or gaskets that fit tightly around the oil filler opening to prevent engine oil leakage, while also avoiding oil vapor escape, keeping the engine compartment clean
Dust and oil protection: prevents dust, impurities, and moisture in the air from entering the engine, protects the purity of the engine oil, avoids wear on engine components caused by impurities, and extends the service life of both the engine oil and the engine
Convenient operation: Mostly designed with a rotary mechanism, no tools are needed to open or tighten, making it easy to operate; the surface usually indicates the engine oil grade for users to easily identify the oil filling position, and some also come with torque indicators to ensure proper tightening