Washers are categorized as follows: Flat Washers (Grade C), Large Flat Washers (Grades A and C), Extra-Large Flat Washers (Grade C), Small Flat Washers (Grade A), Flat Washers (Grade A), Chamfered Flat Washers (Grade A), High-Strength Washers for Steel Structures, Spherical Washers, Conical Washers, Square Taper Washers for I-Beams, Square Taper Washers for Channel Beams, Standard Spring Washers, Light-Duty Spring Washers, Heavy-Duty Spring Washers, Internal-Tooth Lock Washers, Internal-Serrated Lock Washers, External-Tooth Lock Washers, External-Serrated Lock Washers, Single-Tab Lock Washers, Double-Tab Lock Washers, External-Tab Lock Washers, and Lock Washers for Round Nuts.
Flat washers are typically used in assemblies where one connecting component is made of a soft material and the other is made of a hard, relatively brittle material. Their primary function is to increase the contact area, thereby distributing the pressure and preventing the softer material from being crushed. In contrast, the fundamental function of a spring washer is to exert a reactive force against the nut once it has been tightened, thereby increasing the frictional resistance between the nut and the bolt. These washers are manufactured from 65Mn spring steel, heat-treated to a hardness of HRC 44–51, and finished with a surface oxidation treatment.
Lock washers (including spring washers and retaining rings) are elastic components or anti-loosening devices designed to prevent bolts from becoming loose. The working principle of an anti-loosening washer is quite simple: it consists of two mating washer halves. The outer surfaces feature radial ribs, while the inner surfaces feature inclined serrations. During assembly, the inner serrated surfaces face each other, while the outer radial ribs engage firmly with the contact surfaces of the connected components. Should the assembly be subjected to vibration-creating a tendency for the bolt to loosen-relative sliding is permitted only between the inner serrated surfaces of the two washer halves. This relative movement generates a lifting tension, thereby achieving a 100% locking effect.
Spring washers are widely utilized in both load-bearing and non-load-bearing structures within general mechanical products. They are characterized by their low cost and ease of installation, making them particularly suitable for applications that require frequent assembly and disassembly. Washers are indeed listed in the *Kuaiyiyou* automation selection catalog; however, the anti-loosening capability of spring washers is quite low. Their usage rate is particularly low in products-especially those in Europe and the Americas-that demand high reliability; specifically, they have long since been abandoned for use in critical load-bearing structural connections. While our country still sees some application of them in the defense industry, the materials used have been upgraded to stainless steel. Steel spring washers have, in fact, long been prohibited from use within CASC (China Aerospace Science and Technology Corporation)! They are considered highly unsafe for two primary reasons: (1) the "expansion ring" effect, and (2) hydrogen embrittlement.
In the fastener industry, spring washers are commonly referred to as "spring pads." They are manufactured from two primary materials: stainless steel and carbon steel (the latter being essentially iron). The most commonly used standard sizes for spring washers include M3, M4, M5, M6, M8, M10, M12, M14, and M16. The relevant national standard for spring washers is GB/T 94.1-87, which specifies the dimensions for standard-type spring washers ranging from 2 mm to 48 mm. This standard references GB 94.4-85, titled *Technical Conditions for Elastic Washers: Spring Washers*.