The 12.9 Hex Bolt is an ultra-high-strength industrial fastener made from high-quality alloy steel through a tempering and quenching heat treatment process. It possesses excellent tensile strength, yield strength, and fatigue resistance, making it suitable for heavy equipment and structural engineering projects with stringent requirements for connection strength and fastening reliability.
The bolt head features a standard hexagonal design, is compatible with universal wrenches, facilitates installation, and offers high thread precision. It can be used with nuts and washers of the same specification and is widely used in engineering machinery, wind power equipment, automotive manufacturing, mining machinery, pressure vessels, and other fields.
Grade 12.9 represents the mechanical performance indicators of the bolts, with specific parameters as follows:
Tensile Strength: ≥ 1200 MPa
Yield Strength: ≥ 1080 MPa (Yield Strength to Tensile Strength ratio is 0.9)
Hardness Range: 39~44 HRC (Rockwell Hardness)
Shear Strength: ≥ 920 MPa
Material Standards
Commonly used alloy structural steels such as 40Cr, SCM435, and 35CrMo are selected. Stainless steel materials (such as 316L) can be customized according to customer needs to adapt to corrosive conditions.
We offer two finishes: black oxide (per ISO 10683) for a sleek look and mild corrosion resistance, and zinc-nickel plating (8-12μm, per ASTM B841) for better protection in damp environments. The zinc-nickel coating passed 1000-hour salt spray tests (ASTM B117) with only minor spotting, outlasting standard zinc plating by 3x.
Our threading is done with precision rolling (not cutting), which increases thread strength by 30%. UNC/UNF threads (ASME B1.1) have a Class 3A fit, so they seat perfectly with matching nuts, and we add a light oil coating to prevent galling during installation. Every bolt gets a hardness test (Rockwell C 38-42, ASTM E18) before shipping.
As a Chinese manufacturer with 10 years supplying European automotive and machinery clients, we run 6 heat-treated production lines and 4 CNC threading machines, churning out 4,500 tons annually. Our raw material goes through quenching and tempering at 500-550°C to lock in strength, with each batch tested via ultrasonic (ASTM E164) to check for internal flaws.
We keep 300-500 tons in stock at our Suzhou warehouse, covering sizes from M6 to M30 and lengths 20mm to 300mm. Inventory updates in real time on our website, and FOB Shanghai shipments for in-stock 12.9 Hex Bolts leave within 7 days-critical for meeting tight production schedules.
Orders over 50 tons get a 7% discount, plus free zinc-nickel plating and 26% of sea freight.
Here's our guarantee: If any 12.9 Hex Bolt fails to meet the 1220 MPa tensile standard or strips under proper installation, we'll replace them within 3 days and refund all shipping costs. We also offer a 30-day price lock on confirmed orders, with a 3% loyalty discount for repeat buyers within 90 days.
Grade Definition
A high-strength metric bolt classified by the ISO 898-1 standard, where:
Alloy steel (typically chromium-molybdenum steel, e.g., 42CrMo4 or 35CrMo; high carbon content ~0.30–0.45% C for heat treatment response)
Heat Treatment
Quenched and tempered
Mechanical Properties
Tensile Strength: Min. 1200 MPa (174 ksi)
Yield Strength: Min. 1080 MPa (156 ksi)
Hardness: 38–43 HRC (Rockwell C scale, much harder than low/medium-strength bolts)
Elongation: Min. 9% (ductility to resist sudden fracture)
Design & Dimensions
Shape: Hexagonal head (6-sided) for wrench/socket tightening, per ISO 4017 (general purpose) or ISO 4014 (heavy hex for structural use).
Threads: Metric coarse (ISO metric) or fine threads, fully threaded or partially threaded (shank + thread length).
Sizes: M5 to M36 (common); larger sizes available for specialized use.
Surface Finish
Black oxide: Thin protective layer, for indoor/machine environments (moderate corrosion resistance).
Zinc-plated: Improved rust resistance in dry/humid settings (clear, blue, or yellow passivation).
Phosphate coating: For use with lubricants or paints (enhances adhesion).
Chrome plating: For aesthetic and high-corrosion resistance in demanding environments (rare, due to cost).
Applications
Heavy machinery: Engine components, gearboxes, hydraulic systems (high torque/load).
Automotive: Critical joints in engines, transmissions, suspension (high stress areas).
Aerospace: Lightweight but high-strength connections in aircraft frames.
Tooling: Molds, presses, and industrial equipment (precision and durability required).
Structural engineering: High-load joints where failure risk is critical (e.g., crane booms).
Key Features
Ultra-high strength: Among the strongest commercial bolts, ideal for extreme load/torque applications.
Precision: Tight dimensional tolerances for consistent performance in critical joints.
Heat resistance: Maintains strength at moderate elevated temperatures (up to ~300°C, depending on alloy).
Caution: Brittle compared to lower grades; requires proper torqueing to avoid overloading or thread stripping.
Standards Compliance
ISO 898-1: Defines mechanical properties for high-strength bolts (including grade 12.9).
ISO 4014/4017: Specifies dimensions for hex head bolts (general and heavy duty).
DIN 912: German standard equivalent for socket head cap screws (often grade 12.9).
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