ISO Class 8.8 Bolts
Property Class 8.8 bolts per ISO 898-1 — medium carbon steel, quenched and tempered, 800 MPa minimum tensile (830 MPa above M16), 640 MPa yield, 22–32 HRC. The general-purpose high-tensile metric grade.
Last updated: 2026-11
Specifications
Class 8.8 is the workhorse metric high-tensile grade: the default for machine construction, steel framing, automotive components and general engineering where a marked, testable strength class is required. The designation encodes the strength — 8 × 100 MPa tensile, with the .8 meaning yield at 80% of tensile. It is quenched and tempered medium carbon steel, stocked in every standard size from M5 to M64, and accepts all common finishes including hot-dip galvanizing.
| Standard | ISO 898-1, property Class 8.8 (hex bolts per ISO 4014/4017) |
|---|---|
| Material | Medium carbon steel, quenched and tempered |
| Tensile strength, min | 800 MPa (≤ M16); 830 MPa (> M16) — 116,000 psi |
| Yield strength (min) / proof load | 640 MPa yield (≤ M16); 660 MPa (> M16); proof load 580 MPa |
| Hardness | 22–32 HRC |
| Size range | Standard metric sizes M5–M64 widely stocked |
| Typical applications | Machine construction, structural connections, automotive components, general engineering |
| Finishes | Plain, zinc plate, hot-dip galvanized — all compatible |
Where this grade fits
Class 8.8 sits below the ~1000 MPa threshold where hydrogen embrittlement becomes a design constraint, so it keeps the full coating freedom — plain, zinc plate and hot-dip galvanizing are all routine choices. If the joint calculation is comfortably within its 800 MPa capability, this is the more forgiving grade: less notch-sensitive in fatigue and undemanding on coating practice.
Deep read: Hydrogen Embrittlement in High-Strength Bolts: Which Grades Need Controls, Which Coatings and Baking Schedules Are Acceptable, and What to Require Before the RFQ · Calculating Bolt Preload and Clamp Force: Torque, Friction and Tightening Method
Materials
- Medium carbon steel (quenched and tempered)
Ordering & documentation
Documents
Shipments are backed by Mill Test Certificate (MTC), Dimensional Report, Salt Spray Test Report on request, with full batch traceability from raw material to finished product. Quality management follows the owner-confirmed compliance list: ISO 9001:2015, RoHS, REACH. Exact document sets are confirmed on the order.
Quotation
- The fastener family (ISO Class 8.8 Bolts) plus the standard designation from your drawing — DIN / ISO / JIS / ASTM / ANSI, or a drawing for custom parts.
- Size (diameter and length), thread type (metric or inch), property class or grade, and coating or finish.
- Quantity per size and your target delivery date.
- Destination country, and any required documents (for example a mill test certificate) so the quote includes them.
Sample & supply
Minimum order quantity is 1,000–10,000 pieces depending on size. Stock items run 3–7 days. High-strength and custom parts run 15–25 days. Quantities or variants outside the standard range are confirmed at quotation.
Storage & shipping
Parts are packed for export and shipped factory-direct to buyers in Europe, Asia, the Americas and the Middle East. Store fasteners dry and protected until installation, and keep coated parts in their packaging until use; specific packing and preservation requirements can be stated on the order and confirmed at quotation.
Frequently asked questions
Is Class 8.8 equivalent to SAE Grade 5 or Grade 8?
Neither exactly. Class 8.8 (800 MPa minimum tensile ≈ 116,000 psi) sits between SAE Grade 5 (120,000 psi) and Grade 8 (150,000 psi); the common "8.8 ≈ Grade 5" shorthand is approximate because the test methods and proof-load definitions differ. Never substitute one for the other on a drawing that names a specific standard — order the class the specification calls out.
What is the MOQ and lead time for this bolt grade?
The minimum order quantity is 1,000–10,000 pieces depending on size. Stock items ship in 3–7 days; high-strength and custom parts in 15–25 days. Common diameters in this grade are widely stocked; confirm the exact schedule against quantity and size mix at quotation.
What should an RFQ for this bolt grade state?
State the standard and grade (for example ISO 4017 Class 8.8 or ASTM F3125 Grade A325 Type 1), diameter and length, thread type (metric coarse or UNC/UNF), finish (plain, zinc, or hot-dip galvanized where the grade permits), required certificates such as a mill test report per EN 10204 3.1, and quantity per size — plus destination country.
Related knowledge
- What Bolt Property Classes 8.8, 10.9 and 12.9 Encode — and When High Strength Stops Being the Right Choice
- Bolt Grade Selection: ISO 898-1 8.8/10.9/12.9 vs ASTM A307 and A325
- 8.8 vs 10.9 vs 12.9 Bolts: Strength, Hardness and Cost — What the Evidence Settles
- Calculating Bolt Preload and Clamp Force: Torque, Friction and Tightening Method
- How to Determine Tightening Torque and Choose a Tightening Method for a Bolted Joint
- Fastener Failure Modes: Which Fatigue, Creep and SCC Controls the Evidence Supports
- Hydrogen Embrittlement in High-Strength Bolts: Which Grades Need Controls, Which Coatings and Baking Schedules Are Acceptable, and What to Require Before the RFQ
Request a Quote
Get factory-direct pricing from the manufacturer.
What to include in your inquiry
- ✓ Standard and property class (e.g. DIN 912, ISO 4762, class 8.8) — or a drawing for custom parts.
- ✓ Sizes, lengths and thread type (metric or inch).
- ✓ Quantity per size and your target delivery date.
- ✓ Destination country, plus any coating or finish requirement.
- ✓ Any documents you need with the shipment (e.g. mill test certificate) so the quote includes them.
- ✓ Your inquiry goes straight to the factory team by email and gets a reply within 24 hours.
- ✓ Factory-direct pricing
- ✓ Standard and custom specifications
- ✓ Factory-direct export to buyers in Europe, Asia, the Americas and the Middle East
- ✓ Full fastener family support