GB/T 32.1-2020 in English

Standard Evolution and Development Background

GB/T32.1-2020, as the core part of the hexagonal head bolt series standard, is inherited from the 1958 GB32 standard system and has gone through versions such as 1976 and 1988. This revision mainly responds to the modern manufacturing precision requirements and material technology development. It is led by the National Technical Committee for Standardization of Fasteners (SAC/TC85) and jointly drafted by 8 units including Zhoushan Zhengyuan and China Machinery Productivity Promotion Center.

Comparison of major technical changes

Analysis of core parameters

1. Type and size characteristics

The standard stipulates that hexagonal head bolts with holes must meet the following requirements

• Thread specification: M6-M48 full range
• Head hole diameter tolerance: min-max values are strictly controlled (such as M6 hole diameter 1.6-1.85mm)
• Length association: >24mm or >10d, Class B tolerance is automatically applied

2. Material and performance matrix

Implementation and application suggestions

1. Key points of design selection

• Give priority to the preferred specifications in Table 1 (M12/M16/M20, etc.)
• Corrosive environments should specify A4-70 stainless steel or passivation treatment
• For dynamic load situations, 10.9-grade bolts + wire locking are recommended

2. Key points of quality control

1. The head aperture needs to be fully inspected with a go/no-go gauge
2. The thread accuracy is controlled according to the medium precision of GB/T9145
3. The surface treatment verifies the coating thickness according to GB/T5267.1

3. Typical application scenarios