1. Standard

　　Each fastener product must involve some standards in several aspects: 　

1) Fastener product size standards: specify the content of the basic size of the product; for threaded products, it also includes the basic size of the thread, thread end, shoulder distance, undercut and chamfer, and the end of external threaded parts Dimensions and other aspects.

2) Standards on the technical conditions of fastener products. Specifically, it includes the following standards:

　　A) Tolerance standards for fasteners: specify product size tolerances and geometric tolerances.

b) Mechanical performance standards of fastener products: specify the marking method of product mechanical performance levels and the content of mechanical performance items and requirements; some fastener products will change this content to product material performance or work performance Aspect content.

　 　c) Standards for surface defects of fastener products: specify the types of product surface defects and specific requirements.　

　　　D) Surface treatment standards of fastener products: specify the types of product surface treatments and specific requirements.

　　　E) Fastener product testing standards: specify the test content of the various performance requirements mentioned above.

3) Fastener product acceptance inspection, marking and packaging standards: specify the qualified quality level and sampling plan of the random inspection items during the factory acceptance of the product, as well as the content of the product marking method and packaging requirements.

4) Standards on the marking method of fastener products: specify the complete marking method and simplified marking method of the product.

5) Other standards of fasteners: such as the standard of fastener terminology, the standard of fastener product weight, etc.

2. Representation method of common thread specifications of fasteners

Coarse common thread specifications are represented by the letter "M" and "nominal diameter". Fine thread specifications are represented by the letter "M" and "nominal diameter X pitch". The unit of measurement is "millimeter" or: mm: no need to specify, When the thread is left-handed, add the letter "LH" after the specification