High Tensile
Fasteners
Manufacturer India
What “High Tensile” Means — ISO 898 Explained
The term “high tensile fastener” in the ISO 898 metric fastener standard refers to property classes 8.8, 10.9, and 12.9 — the three grades above the general-purpose 4.6 and 5.6 grades used in structural applications. The property class designation encodes the mechanical properties directly in the grade number: the first digit divided by 10 gives the approximate UTS in units of 100 MPa (e.g. Grade 12.9: 12 × 100 = 1,200 MPa nominal UTS), and the second digit divided by 10 gives the ratio of proof stress to UTS (e.g. 12.9: 9/10 = 90% of UTS = 1,080 MPa proof stress).
Grade 8.8 (800 MPa nominal UTS, 640 MPa proof stress) is the standard-specification high tensile bolt for structural steel work, bridgework, and general mechanical engineering. Grade 10.9 (1,000 MPa nominal UTS, 900 MPa proof stress) is for higher-load structural connections, tower bolts, and wind turbine structural bolts. Grade 12.9 (1,220 MPa nominal UTS, 1,100 MPa proof stress) is the highest property class in common supply — used for automotive engine bolts, injection moulding clamping systems, and high-precision mechanical joints where bolt stretch-controlled preload is critical.
For high-temperature pressure flange service (ASME B16.5 applications), ASTM A193 B7 alloy steel stud bolts (Cr-Mo steel, 125 ksi / 862 MPa minimum UTS) with ASTM A194 2H heavy hex nuts are the correct specification — not ISO 898 grade bolts, which are not rated above 300°C. Akbar Fasteners manufactures both ISO 898 and ASTM A193/A194 ranges from the same Mumbai facility.
9 = (Proof / UTS) × 10
High Tensile Grade Properties & Identification
Per ISO 898-1 (bolts), ISO 898-2 (nuts), IS 1367 Part 3, and ASTM A193/A194. Sizes M16–M64 for Grade 8.8. Note: Grade 12.9 bolts must never be galvanised — hydrogen embrittlement risk.
| Property Class | Standard | Material | Min UTS (MPa) | Proof Stress (MPa) | Min Elongation | Hardness (HV/HRC) | Head Mark |
|---|---|---|---|---|---|---|---|
| ISO 898 / IS 1367 METRIC BOLTS — CARBON & ALLOY STEEL | |||||||
| Grade 8.8 | ISO 898-1 / IS 1367 | Med. carbon steel | 800 | 640 | 12% | 250–320 HV | 8.8 ⌂ |
| Grade 10.9 | ISO 898-1 / IS 1367 | Alloy steel Q&T | 1000 | 900 | 9% | 320–380 HV | 10.9 ⌂ |
| Grade 12.9 | ISO 898-1 / IS 1367 | Alloy steel Q&T | 1220 | 1100 | 8% | 38–44 HRC | 12.9 ⌂ |
| ASTM A193 / A194 — ALLOY STEEL FOR PRESSURE FLANGES (High Temp) | |||||||
| ASTM A193 B7 | ASTM A193 / ASME | Cr-Mo alloy steel | 862 (125 ksi) | 724 (105 ksi) | 16% | ≤321 HB | B7 |
| ASTM A193 B7M | ASTM A193 / NACE | Cr-Mo controlled HB | 862 (125 ksi) | 724 (105 ksi) | 16% | ≤235 HB NACE | B7M |
| ASTM A194 2H | ASTM A194 / ASME | Carbon steel | — | ≥248 HB | — | 248–327 HB | 2H |
| IS 3757 — STRUCTURAL BOLTS (HSFG) | |||||||
| IS 3757 / 8.8S | IS 3757 / IS 4000 | Alloy steel Q&T | 830 | 660 | 12% | 255–310 HB | 8S ⌂ |
| ISO 3506 — STAINLESS STEEL HIGH TENSILE | |||||||
| A2-70 | ISO 3506-1 | SS 304 strain-hardened | 700 | 450 | 20% | ≤250 HV | A2-70 |
| A2-80 | ISO 3506-1 | SS 304 str-hrd higher | 800 | 600 | 12% | ≤300 HV | A2-80 |
| A4-70 | ISO 3506-1 | SS 316 strain-hardened | 700 | 450 | 20% | ≤250 HV | A4-70 |
| A4-80 | ISO 3506-1 | SS 316 str-hrd higher | 800 | 600 | 12% | ≤300 HV | A4-80 |
⌂ = manufacturer symbol. Grade 12.9 must NOT be hot-dip galvanised. For exotic alloy high-tensile: Monel K500 (≥1000 MPa) · Inconel 718 (≥1241 MPa)
High Tensile Fastener Types
Grade 8.8, 10.9, 12.9, A193 B7, and stainless A2/A4 in all standard fastener forms. M6–M100. Hardness-certified, property-class-marked, and manufacturer-identified per ISO 898-1.
Hex Bolts & Nuts
Full thread (DIN 933 / ISO 4017) and partial thread (DIN 931 / ISO 4014) hex bolts in Grade 8.8, 10.9, and 12.9. Matching ISO 898-2 hex nuts in property class 8, 10, 12 from same certified heat. Property class mark and manufacturer symbol stamped on bolt head and nut face. M6–M100. Hardness certificate on every lot.
ASTM A193 B7 Stud Bolts
Chromium-molybdenum alloy steel fully threaded stud bolts to ASTM A193 B7 for ASME B16.5 pressure flange joints at elevated temperature — carbon steel plant flanges, steam lines, and all pressure service where the standard B7/2H combination is specified. Class 150–2500, M12–M100. Matched ASTM A194 2H heavy hex nuts from same heat.
Structural HSFG Bolts
High-Strength Friction Grip (HSFG) structural bolts to IS 3757 and EN 14399 for structural steelwork preloaded connections — bridgework, industrial buildings, crane rails, and seismic-zone steel structures. Grade 8.8S, M16–M36. Tensile test, proof load test, and hardness certificate per IS 1608. Full torque wrench washers and matching IS 6649 nuts on request.
Stainless HT Bolts & Nuts
ISO 3506-1 stainless steel high-tensile bolts in A2-70 (SS 304, 700 MPa), A2-80 (SS 304, 800 MPa), A4-70 (SS 316, 700 MPa), and A4-80 (SS 316, 800 MPa) — for corrosion-resistant applications requiring strength above the standard A2-50/A4-50 grades. Food processing equipment, pharmaceutical plant, marine deck bolting, and chemical plant structural connections.
Socket Cap Screws 12.9
Hex socket cylindrical head cap screws to DIN 912 / ISO 4762 in Grade 12.9 alloy steel (1,220 MPa) for high-precision mechanical engineering, hydraulic manifold bolting, injection moulding machine clamps, precision tooling, and any application requiring maximum bolt strength in confined-clearance geometry. M3–M36. Black oxide finish standard.
HT Threaded Rods
Grade 8.8 / 10.9 and ASTM A193 B7 full-thread rods to DIN 975. M6–M100, lengths to 3,000mm. For structural concrete anchoring, equipment tie-rods, pre-stressed concrete connections, and high-load suspension systems. B7 threaded rods for elevated-temperature applications where standard Grade 8.8 loses proof stress. COC and MTC on every order.
High Tensile Fastener Applications
Structural, mechanical, and pressure applications where standard grade fasteners cannot provide sufficient preload force, fatigue resistance, or bore-area bolting efficiency.
Steel Structures
Grade 8.8 structural frames
Oil & Gas Flanges
ASME B16.5 carbon steel
Power Generation
steam flange stud bolts
Automotive & Heavy Machinery
socket cap 12.9 precision
Wind Energy
flange bolting precision
Pressure Vessels
cover and manway bolting
Chemical Plant
B7 high-temp process flanges
Infrastructure & Railways
bridge deck HSFG bolts
High Tensile Standards Coverage
Every lot hardness-tested, property class marked, and dispatched with MTC, hardness certificate, and COC. NABL-accredited tensile and proof load testing available.
Complete Documentation Package
Grade & Heat Traceable
Conformance
Per ISO 898-1 / A193
Accredited Lab Reports
TÜV · BV · Lloyds
Grade 8.8, 10.9, 12.9 or
ASTM A193 B7 Now?
Grade · standard · size · thread pitch · finish · quantity · documentation. Akbar Fasteners Pvt. Ltd. responds within 24 hours.
Export: +91 8696 32 4646 · Support: +91 800 9315 333 · export@akbarfasteners.in