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Grade 8.8, 10.9 & 12.9 Bolts and Screws: Recommended Raw Materials for High-Strength Fasteners
2026-06-23
Selecting the correct raw material is the foundation of producing reliable high-strength bolts, screws, hex bolts, and stud bolts. ISO 898-1 defines mechanical property classes for metric fasteners — most commonly Grade 8.8, Grade 10.9, and Grade 12.9. Each grade specifies minimum tensile strength, yield strength, and hardness that only purpose-selected steel, combined with proper heat treatment, can achieve consistently.
Grade 8.8 Bolts & Screws — Medium-High Strength
Grade 8.8 fasteners (minimum tensile strength 800 MPa, yield ratio 0.80) are the most widely used general-purpose structural fasteners worldwide. They cover hex bolts, hex cap screws, carriage bolts, stud bolts, and fully threaded screws for steel construction, automotive assemblies, and general machinery.
Recommended Materials
- 35# Medium-Carbon Steel — Suitable for smaller-diameter fasteners (≤ M16). Cost-effective, adequate hardenability for Grade 8.8 after quench-and-temper (Q&T).
- 45# Medium-Carbon Steel — The most popular choice for Grade 8.8 hex bolts and stud bolts. Good machinability, stable mechanical properties after Q&T.
- 40Cr Alloy Steel — Preferred for larger diameter bolts (M20+). Chromium addition improves hardenability and tensile uniformity across cross-sections.
Heat Treatment & Applications
Quenching & Tempering (Q&T). Typical hardness range: 22–32 HRC. Applications: structural steel connections, automotive chassis, general machinery, flanged joints, wood-to-steel connections.
Grade 10.9 Bolts & Screws — High Strength
Grade 10.9 bolts and screws deliver a minimum tensile strength of 1,040 MPa. They are specified wherever compact, high-clamping-force connections are required — from automotive engines to heavy earthmoving equipment. Common product forms include socket head cap screws, flanged hex bolts, and high-strength stud bolts.
Recommended Materials
- 40Cr Alloy Steel — Standard workhorse for Grade 10.9. Well-known hardenability, widely available, and certified to ISO 898-1 requirements.
- 35CrMo Alloy Steel — Chromium-molybdenum steel with superior toughness and fatigue resistance. Common for bolts and screws under dynamic loading.
- 42CrMo Alloy Steel — Higher carbon content than 35CrMo; provides excellent strength-toughness balance for large-diameter Grade 10.9 hex bolts.
- SCM435 (JIS) — Japanese Industrial Standard equivalent to 35CrMo. Widely used in Asia-Pacific fastener supply chains; excellent consistency.
Heat Treatment & Applications
Quenching & Tempering (Q&T). Typical hardness range: 32–39 HRC. Applications: engine mounting bolts, suspension and drivetrain fasteners, wind-turbine tower bolts, heavy structural connections.
Grade 12.9 Bolts & Screws — Ultra-High Strength
Grade 12.9 is the highest standardised property class for metric fasteners (minimum tensile strength 1,220 MPa). Ultra-high strength demands precision alloy steel with tightly controlled chemistry. These fasteners — primarily socket head cap screws and specialty industrial bolts — are used wherever safety margins and fatigue life are non-negotiable.
Recommended Materials
- 42CrMo4 / 42CrMo Alloy Steel — The global standard choice for Grade 12.9. Excellent hardenability, high fatigue strength, uniform hardness distribution (39–44 HRC after Q&T). Complies with ISO 898-1, DIN EN 10263, and ASTM guidelines.
- SCM440 (JIS) — Japanese equivalent to 42CrMo4. Dominant in East Asian manufacturing; superior surface finish and dimensional tolerances for socket cap screws.
- 35CrMoV Alloy Steel — Vanadium-enhanced for improved wear resistance and creep strength. Selected for high-temperature or high-vibration fastener applications.
- 30CrNiMo8 Alloy Steel — Nickel-chromium-molybdenum steel for extreme-loading conditions. Specified for aerospace-adjacent and critical engineering bolts.
Heat Treatment & Applications
Quenching & Tempering (Q&T) with tight hardness control (39–44 HRC). Applications: disc brake caliper bolts, precision machine tooling, critical structural anchors, socket head cap screws (DIN 912 / ISO 4762), specialty industrial fasteners.
Quick Reference: Grade vs. Recommended Material
| Grade | Min. Tensile Strength | Recommended Materials | Common Product Types | Typical Heat Treatment |
| 8.8 | 800 MPa | 35# / 45# Carbon Steel 40Cr Alloy Steel | Hex Bolt, Hex Cap Screw, Carriage Bolt, Stud Bolt | Quenching & Tempering |
| 10.9 | 1,040 MPa | 40Cr, 35CrMo, 42CrMo SCM435 Alloy Steel | Socket Cap Screw, Flanged Bolt, Stud Bolt | Quenching & Tempering |
| 12.9 | 1,220 MPa | 42CrMo4 / SCM440 35CrMoV Alloy Steel | Socket Head Cap Screw, Industrial Fastener | Q&T (39–44 HRC control) |
About Fujirui Metal — Professional Fastener Manufacturer & Exporter
Fujirui Metal manufactures and exports precision fasteners including high-strength bolts, hex screws, self-drilling screws, stud bolts, and double-ended studs across Grade 8.8, 10.9, and 12.9 . Surface treatment options: Dacromet, Ruspert, hot-dip galvanising, and zinc plating. All products are certified to ISO, DIN, and ASTM standards, with full material test certificates (MTC) available.
