Fastener Teach

II. Manufacturing Process and Precision

1. Thread Machining Precision

• Imported Bolts: Mostly adopt the thread rolling process (instead of cutting). The thread surface has high smoothness (Ra ≤ 1.6μm) and small tooth profile error (≤ 0.02mm), ensuring smooth engagement with nuts during assembly and reducing the risk of thread stripping. Some high-end products also feature "thread coatings" (e.g., PTFE lubricating coating) to reduce tightening resistance.
• Domestic Bolts: High-end domestic products also use the thread rolling process, but ordinary products may use cutting, resulting in lower thread precision (Ra ≥ 3.2μm). Tooth profile deviations may cause "jamming" during assembly. Additionally, some small manufacturers do not calibrate threads, leading to large pitch tolerances among bolts of the same batch.

2. Heat Treatment Technology

• Imported Bolts: Heat treatment (quenching + tempering) uses continuous furnace temperature control with a temperature fluctuation of ≤ ±5℃, ensuring uniform overall hardness of the bolts (e.g., the surface hardness of Grade 12.9 bolts is HRC 38-42, and the hardness difference between the core and surface is ≤ 3HRC), avoiding local embrittlement.
• Domestic Bolts: High-end domestic brands use heat treatment equipment (e.g., German IPSEN vacuum furnaces) on par with imported ones. However, some small manufacturers use "box-type furnaces" with manual temperature control. Uneven temperature may cause "uneven hardness" of bolts, making them prone to fracture under stress.

3. Surface Treatment Process

• Imported Bolts: Surface treatment focuses more on corrosion resistance and wear resistance. Common processes include Dacromet (salt spray test ≥ 500 hours), hot-dip galvanizing (zinc layer thickness ≥ 85μm), and phosphating + oil coating. The coating has strong adhesion and is not easy to peel off.
• Domestic Bolts: Ordinary products mostly use "electrogalvanizing" (salt spray test ≤ 200 hours), with a thin coating that is prone to rust. High-end domestic products also adopt Dacromet or hot-dip galvanizing, but some manufacturers reduce the coating thickness to cut costs, compromising corrosion resistance.

III. Performance Standards and Testing

IV. Application Scenarios and Cost-Effectiveness

V. Supply Chain and After-Sales Service

Imported Bolts

• Advantages: Long brand history (e.g., Germany’s Würth, the United States’ Spiralock) with profound technical accumulation, capable of providing "customized bolts" (e.g., non-standard threads, special coatings).
• Disadvantages: Long delivery cycle (2-4 weeks for sea freight + customs clearance; air freight is required for urgent orders, doubling costs); high prices due to tariffs + transportation fees (imported bolts of the same specification cost 2-5 times more than domestic ones); slow after-sales response (quality issues require sending products back to the original factory for testing, taking 1-2 months).

Domestic Bolts

• Advantages: Fast delivery (domestic factories usually ship within 1-3 days and support small-batch customization); timely after-sales response (quality issues can be directly addressed with manufacturers for returns/exchanges, and some brands provide "on-site technical guidance"); some large domestic manufacturers (e.g., Zhejiang High-Strength, Shanghai Sheng uang) have achieved "import substitution" and can provide bolts equivalent to imported ones, with prices only 10%-20% higher.
• Disadvantages: Quality varies among small manufacturers, requiring careful selection of reliable brands (it is recommended to choose manufacturers with "National Fastener Quality Supervision and Inspection Center reports" and "ISO 9001 quality management system certification"); weak customization capabilities, with special-specification bolts (e.g., large-diameter M50 and above) still relying on imports.

VI. Industry Status and Purchasing Recommendations

• Ordinary Industrial Field (e.g., Grade 8.8 and below, 304 stainless steel bolts): The performance and stability of domestic bolts fully meet requirements, and their cost-effectiveness is far superior to imported ones. There is no need to blindly pursue "imported" products.
• High-End Field (e.g., Grade 12.9 high-strength bolts, special-material bolts): Leading domestic brands (e.g., standard parts factories under AVIC) can produce some products, but there is still a gap with imported brands in terms of "fatigue life" and "adaptability to extreme environments." For critical equipment, it is recommended to prioritize imported bolts or select "high-end domestic alternative brands" and request test reports.

1. Consider Scenario Requirements: For non-extreme environments and non-critical structures → choose domestic bolts (high cost-effectiveness); for extreme environments and critical load-bearing structures → choose imported bolts or high-end domestic brands.
2. Check Standard Compatibility: If the equipment is imported, prioritize bolts that match the original standards (e.g., DIN for German equipment, ANSI for American equipment) to avoid assembly issues caused by thread specification differences.
3. Verify Manufacturer Qualifications: For domestic bolts, prioritize brands with "National Fastener Quality Supervision and Inspection Center certificates" and "ISO 14001 environmental certification" to avoid purchasing "three-no products" (no manufacturer, no quality certificate, no production date) from small factories.