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Dacromet Hex Socket Bolts: Advanced Anti-Corrosion Coating Meets Precision Fastening Design
2026-07-27
Dacromet hex socket bolts represent the convergence of two critical fastener technologies: the Dacromet high-performance anti-corrosion coating system and the cylindrical socket-head (Allen) bolt geometry. Together, they deliver a fastener solution that withstands highly corrosive environments while enabling precise high-torque installation, making them indispensable in automotive, marine, construction, and heavy machinery applications worldwide.
1. Dacromet Coating Technology
Dacromet is a proprietary water-based inorganic coating system originally developed for carbon and stainless steel fasteners. Unlike conventional electroplated zinc, Dacromet employs a chromium-free (or low-chromium) chemical process that forms a tightly bonded multi-layer barrier of zinc and aluminum flakes. The result is a distinctive silver-gray finish that combines aesthetic neutrality with exceptional protective performance.
The three layers work synergistically to provide comprehensive protection:
Zinc-aluminum flake base layer – provides sacrificial (cathodic) protection, corroding preferentially to shield the underlying steel substrate, while aluminum flakes add barrier protection.
Passivation mid-layer – an inorganic chromate/silicate film that seals the metallic flake structure, resisting salt spray, chemical attack, and heat far beyond conventional zinc plating.
Top organic seal coat (optional) – enhances torque-prevention performance and weathering resistance, while producing a consistent silver-gray appearance with low coefficient of friction.
Table 1. Corrosion Resistance Comparison (Salt Spray Test, NSS)
| Coating Type | Salt Spray Hours | Thickness (μm) | Typical Application |
| Dacromet | ≥ 1,000 – 3,000 | 6 – 10 | Marine / automotive |
| Ruspert | ≥ 1,000 – 3,000 | 3 – 5 | Outdoor / marine |
| Zn-Ni alloy plating | ≥ 720 – 1,000 | 8 – 12 | Automotive |
| Conventional Zn plating | 96 – 240 | 5 – 8 | Indoor / general |
2. Hex Socket Bolts
Hex socket bolts, also known as socket head cap screws or Allen bolts, feature a cylindrical head with an internal hexagonal drive. This geometry allows higher torque transmission with a smaller head profile compared to external hex bolts, making them ideal for applications with limited clearance or where a flush, clean appearance is required.
Key design features include:
Cylindrical head with internal hex drive – accepts standard hex keys for high-torque installation with minimal head protrusion; drive sizes conform to ISO 2936 or ASME B18.3.
Full or partial threading – full-thread variants distribute load evenly along the engaged length; partial-thread variants provide a stronger unthreaded shank for shear applications.
High-strength alloy steel (8.8 / 10.9 / 12.9) – heat-treated grades ensure tensile strength up to 1,220 MPa, suitable for dynamic loads and critical joints.
Dacromet surface finish – provides ≥ 1,000 hours of salt-spray protection without hydrogen embrittlement, making it ideal for high-strength fasteners where electroplating is unsuitable.
Table 2. Common Dacromet Hex Socket Bolt Specifications (Property Class 8.8)
| Size | Thread Dia. (mm) | Head Height (mm) | Min. Tensile (MPa) | Typical Application |
| M4 | 4 | 4 | 800 | Electronics / instruments |
| M5 | 5 | 5 | 800 | Light assembly |
| M6 | 6 | 6 | 800 | Furniture / machinery |
| M8 | 8 | 8 | 800 | Mechanical / automotive |
| M10 | 10 | 10 | 830 | Structural joints |
| M12 | 12 | 12 | 830 | Heavy machinery |
3. Summary
Dacromet hex socket bolts combine the superior corrosion resistance of the Dacromet inorganic coating system (achieving 1,000–3,000 hours of salt-spray protection without hydrogen embrittlement) with the high-torque, low-profile design of the hex socket bolt. This integration enables reliable fastening in demanding environments — from chassis and brake systems to marine structures and outdoor equipment — while preserving precise torque control and long-term durability. As industries increasingly demand fasteners that balance performance, safety, and longevity, Dacromet hex socket bolts have become a preferred choice for engineers and OEMs worldwide.
