A cutaway view of a piston ring showing how it fits into the grooves of the piston and interacts with the cylinder wall. Typically, a piston ring is a thin, circular component with a slit along its circumference that allows it to expand and contract against the cylinder wall.

Piston Rings: The body of a piston ring is usually made of a durable material such as cast iron, steel, or a special alloy. It forms a complete circle with a small gap where the two ends meet to allow for thermal expansion.

Ring Groove: The piston has grooves machined into the surface where the piston rings rest. These grooves hold the rings securely in place while allowing them to move freely as the piston reciprocates within the cylinder.

Compression Ring: The top piston ring is called a compression ring. Its main function is to seal the combustion chamber and prevent gas from escaping during the combustion process. It also helps transfer heat from the piston into the cylinder walls.

Second Compression Ring: Some engines have a second compression ring below the top ring. This additional ring further enhances the sealing of the combustion chamber and helps regulate fuel consumption.

Oil Control Ring: Below the compression ring, there is usually an oil control ring assembly. It consists of multiple rings, including a scraper ring and one or more oil control rings. Their purpose is to regulate the amount of oil entering the combustion chamber while scraping excess oil off the cylinder walls to prevent excessive oil consumption and minimize contamination.

Ring End Gap: The small gap between the ends of the piston ring that allows expansion as the engine reaches operating temperature. Proper clearance is critical to preventing the ring from bonding with the cylinder wall, ensuring efficient engine operation and longevity.

Type			Compression Ring
No.			TO-1	TO-2	TO-3	TO-4	TO-5
Cross-section shape
Application	Four-stroke	Gasoline engine	●★	●	●	—	—
		Diesel engine	—	●	●	—	●
	Two-stroke		—	●	●	●
	Air compressor		●	—	●	—	—

No.			TO-6	TO-7	TO-8	TO-9	TO-10
Cross-section shape
Application	Four-stroke	Gasoline engine	●★	●	●	●	●
		Diesel engine	●	●	●	—	●
	Two-stroke		—	—	—	—	—
	Air compressor		●	●	●	●	●

Type			Oil Control Ring
No.			Y1-1	Y1-2	Y2-1	Y2-2
Cross-section shape
Application	Four-stroke	Gasoline engine	●★	●	—	—
		Diesel engine	—	—	●	●
	Two-stroke		—	—	—	—
	Air compressor		●	●	—	—

No.			Y3-1	Y3-2	Y4-1	Y4-2
Cross-section shape
Application	Four-stroke	Gasoline engine	—	●	—	—
		Diesel engine	—	●	—	—
	Two-stroke		—	—	—	—
	Air compressor		●	●	●	●
“●”Indicates that it applies，“—”Not applicable，“★”Indicates typical configuration for gasoline engines.