Here is Standard Size Drywall Screws Supplier talking about Standard Specification for Screws for Fasteners.
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Standard screws are the norms, and each country and department has its own standards. At present, the most commonly used standards in our usual business are the following:
1. GB - China National Standard (GB) ANSI - American National Standard (American Standard)
2. DIN - German National Standard (German Standard) ASME - American Society of Mechanical Engineers Standard
3. JIS - Japanese National Standard (Japanese Standard) BSW - British National Standard
4. GB—The national standard is one of many standards in China. There are also industry standards, professional standards, and departmental standards. National standards are divided into GB (mandatory standards) and GB/T (recommended standards) and GBn (national internal standards). We usually see GB30, GB5783 and so on are mandatory standards.