GB/T 1720-2020 "Circle-drawing Test for Paint Films" is applicable for the determination of paint film adhesion. Using a circle-drawing tester (equipped with a multi-edge cutting blade), the instrument draws concentric circular tracks on the surface of the paint film, cutting through to the substrate. The test is conducted at 23±2°C. After drawing the circles, the coating's peeling condition is observed under a magnifying glass, and the adhesion level is rated on a scale of 0–7. The specifications of the cutting blade, the circle-drawing speed, and the rating criteria are clearly defined. Different levels correspond to the bonding strength between the coating and the substrate, providing a standardized procedure for paint film adhesion testing.