GB/T 39641-2020 in English

Scope of application

This standard is applicable to the parameter detection of fastener threads with a nominal diameter ≥1mm (external thread) and ≥4.8mm (internal thread), including:

• 11 core parameters such as effective mean diameter and basic tooth profile bottom diameter
• Contact measurement method using thread indicating gauge

Technological evolution

Compared with traditional thread gauge detection, this standard innovatively:

Key technical requirements

Test condition control

• Standard reference temperature: 20℃±10℃
• Temperature difference between workpiece and gauge ≤1℃
• Measurement force control: 12N±1N

Probe selection specification

Implementation recommendations

Measurement uncertainty control

Key influencing factors and control measures:

1. Temperature effect: 8.2×10^-6×d_n (d_n is the nominal diameter of the thread)
2. Probe error: The flank angle deviation must be controlled within ±5'
3. Standard gauge: The expanded uncertainty of the center diameter should be ≤1/4 of the measured tolerance

Typical application cases

Example of a certain M10 bolt inspection:

• Use the three-roll through-end probe to inspect triangular prism deformation
• Axial center diameter difference measurement must be performed at both ends of the screwing length
• The comprehensive tooth profile deviation should be ≤30% of the center diameter tolerance