The differences between grade A, B, and C
Hex Bolts primarily lie in tolerance levels, usage scenarios, and manufacturing and installation requirements.
Here’s a summary of the key distinctions:
1. Tolerance Levels
• Grade A: Precision grade, with the smallest tolerance, suitable for applications requiring high precision and strength.
• Grade B: Standard grade, with larger tolerance than grade A, suitable for general strength and precision requirements.
• Grade C: Coarse grade, with the largest tolerance, suitable for applications with rough surfaces and low precision requirements.
2. Manufacturing and Usage
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Grade A and B: Precision
Bolts with smooth surfaces and accurate dimensions. They require high manufacturing and installation standards and are more expensive. Typically used in high-precision assemblies or where the structure is subject to significant impact, vibration, or varying loads.
• Grade C: Coarse bolts with rougher surfaces. Generally used in secondary structures for shear connections, temporary fixing during installation, or in applications requiring tensile connections with low precision demands.
3. Application Range
• Grade A: Used for bolts with a diameter of 1.6-24mm and a length ≤10d or ≤150mm, mainly in important applications requiring high precision.
• Grade B: Used for bolts with a diameter >24mm or length >10d or ≥150mm, suitable for general precision and strength requirements.
• Grade C: Used for bolts ranging from M5 to M64, commonly applied in rough surface scenarios where high precision is not critical.
4. Standards Relevant standards include:
• "High-Strength Bolted Connections for Steel Structures" GB/T3632-1995
• "High-Strength Hex Bolts for Steel Structures" GB/T1228-1991 • Among others.
5. Selection Advice
For general mechanical structures, grade B or C bolts are typically sufficient. Grade A bolts, due to higher costs, are usually reserved for critical components or applications requiring high precision. Understanding these distinctions helps in selecting the appropriate bolts for design and construction, ensuring both safety and cost-efficiency of the structure.
