The basis for distinguishing top or comp rings from a piston ring is that top ring is bright, white, and thick, and the comp ring are dark, black, and thin. That is, top ring is silver white and the comp ring is black. Top ring is brighter than the comp ring, and the top ring is thicker. The comp rings are relatively thin.

The piston ring will have a mark, and generally the side with letters and numbers is facing up. The piston ring is the core component of the fuel engine. It seals the fuel gas with the cylinder, piston, and cylinder wall. Gasoline and diesel engines have different fuel properties, so the piston rings used are also different. The four functions of the piston ring are sealing, oil control (adjusting oil), heat conduction, and guidance. Sealing refers to sealing the gas to prevent the gas in the combustion chamber from leaking to the crankcase to improve thermal efficiency. Oil control is to wipe off the excess lubricating oil on the cylinder wall while covering the cylinder wall with a thin oil film to ensure normal lubrication. Heat conduction is the conduction of heat from the piston to the cylinder liner for cooling.