GEOMET® (Jumete) Coated Hexagonal Bolts-Technical Introduction 

1. Introduction to GEOMET® (久美特) Coating

GEOMET® (commonly known in Chinese as 久美特 or Jumete) is a chromium-free, water-based zinc-aluminum flake coating developed by NOF Metal Coatings Group as an environmentally friendly successor to the traditional DACROMET® process. It provides outstanding corrosion protection for steel fasteners, particularly hexagonal bolts, while fully complying with modern environmental regulations such as RoHS, REACH, ELV (2000/53/EC), and ISO 10683.

The coating consists of passivated zinc and aluminum flakes bound by an inorganic matrix. Applied by dip-spin or spray methods and cured at relatively low temperatures, GEOMET® forms a thin metallic silver-gray film (typically 6–12 μm) that does not significantly affect thread dimensions or fit. Because the process is non-electrolytic, it completely eliminates the risk of hydrogen embrittlement—an important advantage for high-strength bolts (property classes 8.8, 10.9 and 12.9).

1.1 Key Advantages of GEOMET®

• Completely chromium-free (no Cr⁶ or Cr³⁺) and water-based – environmentally responsible manufacturing.
• Excellent salt-spray resistance: 720–1500+ hours (ISO 9227 / ASTM B117) depending on grade and thickness.
• No hydrogen embrittlement – ideal for high-tensile fasteners.
• Thin film (≈ 8 μm average) – does not interfere with bolt-nut assembly or torque values.
• Good thermal stability up to 300 °C and resistance to automotive fluids, solvents and cyclic corrosion.
• Electrical conductivity and bimetallic compatibility with aluminum.
• Approved by major OEMs: Toyota, Honda, VW, BMW, GM, Ford, Daimler, Fiat, etc.

1.2 Main GEOMET® Grades

Table 1 – Comparison of Common GEOMET® Coating Systems

Note: Actual performance depends on coating weight (typically >24 g/m²), substrate preparation, and optional PLUS® topcoats that further adjust friction coefficient (μ ≈ 0.06–0.20 per ISO 16047).

2. Hexagonal Bolts – Design and Standards

Hexagonal (hex) head bolts are among the most widely used mechanical fasteners. Their six-sided head allows easy tightening with standard wrenches or sockets and provides a large bearing surface. When combined with GEOMET® coating, these bolts deliver both high mechanical strength and superior long-term corrosion resistance.

2.1 Relevant International Standards

• ISO 4014 / DIN 931 – Hexagon head bolts with partial thread (shank under head).
• ISO 4017 / DIN 933 – Hexagon head screws fully threaded.
• ISO 898-1 – Mechanical properties of fasteners made of carbon steel and alloy steel (property classes 4.6 to 12.9).
• ISO 10683 – Non-electrolytically applied zinc flake coatings on fasteners (directly applicable to GEOMET®).
• ASTM F1136 / F1136M – Zinc/Aluminum Corrosion Protective Coatings for Fasteners.

2.2 Mechanical Property Classes (ISO 898-1)

Table 2 – Common Property Classes for Steel Hex Bolts

GEOMET® coating is especially valuable for classes 10.9 and 12.9 because the non-electrolytic process avoids hydrogen embrittlement that can occur with conventional electro-galvanizing.

2.3 Typical Dimensional Ranges

Metric hexagonal bolts are commonly supplied in diameters from M5 to M36 (and larger on request). Thread pitch follows ISO metric coarse series. Partial-thread bolts (ISO 4014) leave an unthreaded shank that improves shear strength; full-thread bolts (ISO 4017) maximize engagement in tapped holes.

3. Performance Data & Coating Characteristics

3.1 Corrosion Resistance Data

Table 3 – Typical Neutral Salt Spray (NSS) Performance (ISO 9227 / ASTM B117)

Cyclic corrosion tests (e.g., GMW 14872, SAE J2334, ACT) also show excellent results—typically 60 cycles or more without red rust when properly applied.

3.2 Additional Functional Properties

1. Temperature resistance: Performance retained after 100 h at 180 °C; usable up to ≈ 300 °C for short periods.
2. Chemical resistance: Good resistance to fuels, oils, brake fluid, coolants and many organic solvents (VDA 621-412).
3. Mechanical durability: Excellent resistance to handling damage and multiple tightening cycles when lubricated topcoats are used.
4. Paintability: Compatible with most organic coatings and powder paints.

3.3 Comparison with Alternative Coatings

Table 4 – GEOMET® vs. Other Common Fastener Coatings

4. Applications and Selection Guidelines

GEOMET®-coated hexagonal bolts are widely specified in industries where long-term corrosion protection, environmental compliance and reliable mechanical performance are required simultaneously.

4.1 Typical Application Fields

• Automotive: chassis, suspension, powertrain, under-body fasteners (approved by VW, BMW, GM, Toyota, Honda, etc.).
• Construction & infrastructure: steel structures, bridges, rail, wind-turbine towers.
• Agricultural and construction machinery.
• Electrical and electronic enclosures where conductivity and corrosion resistance are both needed.
• General industrial equipment exposed to humidity, salt or cyclic temperatures.

4.2 Selection Recommendations

When specifying GEOMET® hexagonal bolts, consider the following:

1. Required corrosion class → choose GEOMET 321 (standard), 500 (friction-controlled) or 720 (maximum protection).
2. Mechanical strength → select property class 8.8, 10.9 or 12.9 according to load and safety factors.
3. Thread type → partial thread (ISO 4014) for shear-critical joints; full thread (ISO 4017) for maximum engagement.
4. Friction coefficient → specify PLUS® topcoat if controlled torque-tension relationship is critical.
5. Environmental & regulatory requirements → GEOMET® satisfies RoHS, REACH and ELV without additional exemptions.

4.3 Quality Assurance Notes

Reputable coating applicators maintain process certifications (ISO 9001) and often hold OEM approvals (Toyota, GM, etc.). Coating thickness, adhesion (tape test), salt-spray performance and friction coefficient should be verified according to ISO 10683 and customer drawings. Visual appearance is a uniform metallic silver-gray; black variants (GEOBLACK®) are also available when aesthetics or identification require it.

5. Conclusion

GEOMET® (久美特) coated hexagonal bolts combine the proven mechanical reliability of ISO-standardized hex-head fasteners with a modern, chromium-free zinc-aluminum flake coating that delivers exceptional corrosion protection, environmental compliance and freedom from hydrogen embrittlement. Whether used in automotive chassis, structural steelwork or industrial machinery, these fasteners offer a technically superior and future-proof solution for demanding applications.

For project-specific recommendations, coating specifications or mechanical property data, consult the relevant ISO standards (4014, 4017, 898-1, 10683) and the technical data sheets issued by NOF Metal Coatings Group or authorized applicators.