High Tensile Bolt
Grades Explained
Mumbai · India
Why There Are Two Bolt Grading Systems in High Tensile Bolt Grades Explained
ISO 898-1 and SAE J429 developed on separate continents to solve the same underlying problem — giving a bolt a stamped, verifiable indication of its mechanical strength — but neither system was designed with the other in mind. ISO 898-1 uses a two-part number (8.8, 10.9, 12.9) where the first digit ×100 gives approximate tensile strength in MPa and the second digit ÷10 gives the yield-to-tensile ratio. SAE J429 instead uses radial lines cast or forged onto the bolt head — three lines for Grade 5, six lines for Grade 8 — a marking convention that has nothing numerically in common with the metric system’s digits.
The practical consequence is that a bolt marked “8.8” and a bolt with three radial lines are not directly comparable by simply reading the marking — you have to know what each marking means in terms of actual tensile strength before you can judge whether they’re functionally equivalent. This becomes a real issue for buyers sourcing across both metric and imperial supply chains, replacing a bolt in an assembly originally specified to the other system, or verifying a mixed shipment where both marking types appear on the same purchase order.
Akbar Fasteners Pvt. Ltd. exports to over 50 countries, and our high tensile bolt range covers both ISO 898-1 metric property classes and SAE-equivalent grades, manufactured with the same ISO 9001:2015 quality system and full mill test documentation regardless of which marking convention the order requires.
One Supplier Across Both Systems
Metric and SAE-Equivalent Grades
Both ISO 898-1 property classes and SAE J429-equivalent grades manufactured under the same quality system.
Correct Head Marking Applied
Bolts forged with the correct marking convention for the specified grading system — numbers or radial lines, not a mismatch.
Cross-Reference Support
We help confirm the correct equivalent grade when a drawing or existing assembly references the other system.
Full Mill Test Traceability
Every batch traceable by heat number with mechanical property verification confirming true grade compliance.
Head Marking Identification Guide
8.8
Two numbers separated by a period. 800 MPa minimum tensile strength, 0.8 yield-to-tensile ratio. Common general-purpose metric grade.
10.9
1040 MPa minimum tensile strength, 0.9 yield-to-tensile ratio. Higher-strength metric grade for demanding structural bolting.
12.9
1220 MPa minimum tensile strength, 0.9 yield-to-tensile ratio. Maximum standard metric strength class, typically automotive/machinery use.
Grade 5 — Three Radial Lines
Approximately 120 ksi (830 MPa) minimum tensile strength. The most common SAE inch-series high strength grade.
Grade 8 — Six Radial Lines
Approximately 150 ksi (1035 MPa) minimum tensile strength. Higher-strength SAE grade for demanding automotive and machinery joints.
Grade 2 — No Markings
Approximately 74 ksi (510 MPa) minimum tensile strength, size dependent. Unmarked head indicates the lowest standard SAE grade.
Metric Class to SAE Grade Equivalence
The two systems don’t map onto each other perfectly, but for practical strength-matching purposes, these are the pairings buyers most often use when cross-referencing between metric and SAE inch-series bolting. Always verify the specific application’s requirements rather than substituting purely on approximate strength alone.
| Metric Class (ISO 898-1) | Approx. Tensile | Nearest SAE Grade (J429) | Approx. Tensile (SAE) |
|---|---|---|---|
| Class 4.6 | 400 MPa | Grade 2 | ~510 MPa (74 ksi) |
| Class 8.8 | 800 MPa | Grade 5 | ~830 MPa (120 ksi) |
| Class 9.8 | 900 MPa | Grade 5 / Grade 5.2 | ~830 MPa (120 ksi) |
| Class 10.9 | 1040 MPa | Grade 8 (closest) | ~1035 MPa (150 ksi) |
| Class 12.9 | 1220 MPa | No direct SAE equivalent | Exceeds standard Grade 8 |
High Tensile Grade Range
Class 8.8 / 10.9 / 12.9
Full metric property class range with forged head marking per ISO 898-1.
Cr-Mo Alloy SteelASTM A193 Grade B7
125 ksi minimum tensile alloy steel stud bolt grade for pressure and process bolting.
Sour ServiceASTM A193 Grade B7M
Hardness-controlled variant of B7 for NACE-qualified sour service applications.
Matching RangeMatching Nuts & Washers
Correctly rated nuts and washers to pair with each grade for a properly matched joint.
Application Areas
Wherever metric and imperial-specified equipment coexist on the same project.
Automotive & Machinery
in imported and local components
Structural Steelwork
bolting specifications
Multinational Manufacturing
metric and imperial standards
Import/Export Trade
across international shipments
Heavy Equipment Servicing
mixed-origin equipment fleets
Maintenance & Repair
replacing unmarked or unknown bolts
Engineering Procurement
across international drawings
General Engineering
across mechanical assemblies
Standard Export Documentation
Prepared as standard practice regardless of grading system specified.
Mill Test Certificate (MTC)
Heat number, chemical composition, and mechanical property verification for every lot.
Certificate of Conformance
Confirms the shipment matches the purchase order specification and grade in full.
Certificate of Origin (COO)
Confirms India as country of manufacture for destination customs purposes.
Commercial Invoice & Packing List
Itemized value, Incoterm, and detailed carton/weight breakdown for customs clearance.
NABL Accredited Test Reports
Independent tensile, hardness, and proof load testing available on request for critical applications.
Bill of Lading
Ocean or air freight shipping document confirming carrier, mode, and consignee details.
Internationally Recognised Standards Coverage
Related Fastener Grades & Materials
High Tensile Bolts Specifications
The full detailed specification breakdown for property class 8.8, 10.9, and 12.9 bolting.
View High Tensile Specs →ASTM A193 Grade B7 Stud Bolts
High-strength alloy steel stud bolt grade for pressure and process bolting.
View Grade B7 →Different Types of Nuts and Bolts
A guide to bolt head and nut designs across every standard fastening application.
View Nut & Bolt Types →Fastener Applications By Industry
A broader guide to matching fastener material grades to the right industry and environment.
View Applications Guide →Need Help Cross-Referencing
a Grade?
Tell us the marking you’re seeing or the specification your drawing calls for — we’ll confirm the correct equivalent grade. Akbar Fasteners Pvt. Ltd. responds within 24 hours.
Sales: +91 724 0000 733 · Support: +91 800 9315 333 · sales@akbarfasteners.in