GB/T 131-1993 is a standard for the representation of surface roughness in mechanical drawing. It specifies the symbols of surface roughness, including basic symbols, extended symbols, etc., and clearly defines the meaning of each symbol. Make clear the code composition and labeling rules, covering different asperity parameters represented by the combination of numbers, letters and symbols. Detail the position and method of surface roughness symbols, code numbers on part drawings and assembly drawings in mechanical drawing. The standard unifies drawing specifications, enabling engineers to accurately express the surface mass requirements of parts and ensure the accuracy of mechanical product manufacturing and assembly