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ISO 9001:2015 · ISO 898-1 Grades 4.6–12.9 · ASTM A307/A325/A490

Carbon Steel Fasteners Manufacturer, Supplier & Exporter for Quality Fastening Solutions

Carbon steel fasteners are the most widely used industrial fasteners globally. We manufacture ASTM A307, A325, A490 and metric Grade 8.8, 10.9, 12.9 fasteners for construction, infrastructure, automotive, and heavy machinery industries.
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7

Grades

42

Products

-20°C

Min Temp

370°C

Max Temp

1220 MPa

Min tensile strength · Grade 12.9 per ISO 898-1

Low

Hot-dip galvanized / zinc-plated / plain black

7.85 g/cm³

Density · structural carbon steel

The structural & general-purpose steel fastener explained

What is Carbon Steel Fasteners?

Carbon steel fasteners are the most widely manufactured and economical fastener group, produced from plain carbon or micro-alloyed steel to ISO 898-1 metric property classes (4.6 to 12.9) and ASTM A307, A325 and A490 structural specifications. The mechanical properties — from 400 MPa tensile (Class 4.6) to 1220 MPa (Class 12.9) — are achieved through controlled carbon content (0.15–0.55%) and quench-and-temper heat treatment for the higher grades. Carbon steel fasteners are the standard for structural steel connections, civil engineering, general machinery, automotive assemblies and industrial equipment where moderate strength is required at minimum cost. Surface protection — hot-dip galvanizing, zinc electroplating, geomet or phosphate coating — is applied to offset the inherent corrosion susceptibility. Class 8.8 hex bolts with ISO 4032 nuts are the most commonly specified combination for structural connections worldwide.
PropertySpecification
Base ElementIron (Fe) + Carbon
C Content0.15–0.55%
Grade Range4.6, 8.8, 10.9, 12.9 / A307, A325, A490
Max Tensile1220 MPa (Cl.12.9)
Density7.85 g/cm³
StandardsISO 898-1, ASTM A307/A325/A490

Carbon Steel grades — which do you need?

Multiple fastener grades of Carbon Steel Fasteners serve diverse industrial fasteners and engineering applications, with each grade offering distinct mechanical properties, corrosion resistance, temperature capability, and strength characteristics. Compare available material grades to support precise material selection aligned with specific operating environments, industry standards, and engineering performance requirements.

Grade UNS Tensile (min) Key Property Max Temp Best Application
Metric Grade 8.8 ISO Class 8.8 800 MPa General structural 200°C Construction, machinery View grade
Metric Grade 10.9 ISO Class 10.9 1040 MPa High strength 200°C Wind towers View grade
Metric Grade 12.9 ISO Class 12.9 1220 MPa Precision clamping 200°C Tooling, precision engineering View grade
ASTM A307 A ASTM A307 Grade A 414 MPa Low carbon 260°C General construction View grade
ASTM A307 B ASTM A307 Grade B 414 MPa Threaded rods, flanges 260°C Piping, industrial equipment View grade
ASTM A325 ASTM A325 825 MPa Structural bolting 370°C Bridges, steel frames View grade
ASTM A490 ASTM A490 1040 MPa Ultra-high structural strength 370°C Heavy steel construction View grade
ASTM A307 Grade A
ASTM A307 Grade B
ASTM A325
ASTM A490
Metric Grade 10.9
Metric Grade 12.9
Metric Grade 8.8

Carbon Steel Fasteners — International Standards & Material Certifications

Carbon Steel Fasteners from RealBolt Engineering Industries are manufactured to ISO 898-1 Classes 4.6 through 12.9, EN 14399 for structural bolt assemblies, and EN ISO 4014/4017 dimensional standards. All batches ship with EN 10204 MTC 3.1; hardness test certificates and dimensional inspection reports are provided as standard with every carbon steel fastener order.
Standards
DIN 931 DIN 933 DIN 960 DIN 961 DIN 912 DIN 6912 DIN 6914 DIN 7990 DIN 938 DIN 939 DIN 976-1 DIN 934 DIN 980 DIN 982 DIN 985 DIN 439 DIN 315 DIN 557 DIN 562 DIN 125A DIN 126 DIN 127 DIN 128 ISO 4014 ISO 4017 ISO 8676 ISO 8765 ISO 4032 ASME B18.2.1 ASME B18.3 ASME B18.31.2 ASME B18.2.2 ASME B18.21.1 EN 14399 EN 15048 EN ISO 4014 EN ISO 4017 EN ISO 4032 BS EN ISO 4014 BS EN ISO 4017 BS EN ISO 4032 BS 1768 BS 3692 BS 4190 IS 1363 IS 1364 IS 1367 IS 3757 SAE J429 SAE J995 SAE J1199 UNI 5737 UNI 5739 UNI 5588 CSN 021101 CSN 021103 CSN 021123 PN 82101 PN 82105 PN 82144
Certifications
ISO 9001:2015 ASTM Certified NABL Lab ISO 898-1 MTC 3.1 / 3.2

Carbon Steel Fasteners Applications — Industries & Use Cases

Carbon Steel Fasteners from RealBolt Engineering Industries are specified by engineers and procurement teams across demanding industries where high strength at minimum cost for structural steel connections, general machinery, and construction fastening applications is critical to fastener performance and service life. Primary end-use sectors for Carbon Steel Fasteners include civil and structural engineering, infrastructure bridges and highways, general machinery, wind energy towers, and automotive — click each industry below to see specific application details and recommended grades.
ISO 898-1 Class 8.8 and 10.9 bolts with ISO 4032 nuts are specified for structural steel connections in buildings, bridges and towers per EN 1993 (Eurocode 3). ASTM A325 and A490 are the US equivalents for AISC-designed steel structures.
ASTM A325 Type 1 (medium carbon) and A490 high-strength structural bolts are used in highway bridge main member connections, expansion joints and cable-stay anchor hardware.
ISO 898-1 Class 8.8 and 10.9 socket-head cap screws and hex bolts are the workhorse fasteners for machine tools, presses, conveyors and production equipment across all manufacturing industries.
Class 10.9 and 12.9 high-strength bolts are used for wind turbine tower section flange connections and nacelle base ring joints. Hot-dip galvanized or geomet-coated for corrosion protection in outdoor service.
Class 10.9 and 12.9 bolts are extensively used in automotive engine assemblies, suspension components, wheel hub bolting and heavy commercial vehicle chassis connections.

Carbon Steel vs Alloy Steel vs Stainless Steel

This comparison table helps structural engineers, procurement managers, and project estimators evaluate Carbon Steel Fasteners against Alloy Steel and Stainless Steel Fasteners based on proof load, minimum tensile strength, maximum operating temperature, corrosion resistance, hot-dip galvanizing compatibility, applicable design code, and relative cost per bolt — ensuring the most cost-effective specification for each application. Use this data to make an informed alloy selection for your specific operating environment, design code, and budget — or contact RealBolt’s technical team for a project-specific recommendation.
Property Carbon Steel 8.8 Alloy Steel B7 SS 316L
Max service temp 200°C 427°C 800°C
Tensile strength (min) 800 MPa 862 MPa 485 MPa
Corrosion resistance Very Low Low Good
HDG compatible Yes (Class <=8.8) Limited N/A
Relative cost Lowest Low-Medium Medium
NACE MR0175 compliant No Conditional Conditional

Verdict: Carbon Steel 8.8 is the economical default for general structural assemblies with applied corrosion protection. Alloy Steel B7 is chosen for process plant high-temperature bolting. SS 316L is specified where moderate corrosion resistance is needed.

Need Carbon Steel fasteners? Get a competitive price today.

Partner with RealBolt Engineering Industries for certified Carbon Steel Fasteners backed by full EN 10204 material test reports, competitive pricing, and reliable global delivery from our Mumbai facility. Our technical and commercial team supports specification across ASTM A307, A325, A490, and ISO 898-1 Classes 8.8 through 12.9 Carbon Steel Fasteners — supplying in plain black, zinc-plated, hot-dip galvanized, geomet-coated, and mechanically galvanized finishes in sizes M6–M100 and ¼″–4″ with hardness test reports and dimensional inspection certificates. Request a quote today and receive a competitive price within 24 hours.
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Carbon Steel Fasteners — Common Questions Answered by Our Technical Team

Browse the expert answers below to the most frequently asked questions about Carbon Steel Fasteners — covering 8.8 vs 10.9 vs 12.9 selection, ASTM A325 vs A490 vs ISO 10.9 differences, galvanizing and hydrogen embrittlement risk, surface finish options, structural bolt torque-tension values, and documentation including ISO 898-1 and ASTM A325 compliance certificates. If your question is not answered here, contact the RealBolt technical team directly for grade-specific guidance, project support, and competitive pricing on Carbon Steel Fasteners.
ISO 898-1 Class 8.8 bolts have 800 MPa tensile strength and 640 MPa yield (proof load). Class 10.9 bolts have 1040 MPa tensile and 940 MPa yield — approximately 30% stronger. Class 8.8 is used for general structural bolting; Class 10.9 is used where higher preload is required, such as friction-grip joints, heavy machinery and wind turbine tower flanges.
We supply carbon steel fasteners in: plain black (as-machined), zinc electroplated (5–12 µm, ASTM B633), hot-dip galvanized (HDG, 45–85 µm, ASTM A153 / ISO 1461), mechanically galvanized (ASTM B695), geomet/delta-tone coated, and plain phosphated + oiled. HDG is not recommended for Class 10.9 and 12.9 due to hydrogen embrittlement risk.
ASTM A325 is the US standard for high-strength structural hex bolts (825 MPa min tensile), equivalent to approximately ISO 898-1 Class 8.8 in strength but with different chemical composition and testing requirements. Used in AISC-designed structural steel connections. ASTM A490 (1040 MPa) is the high-strength equivalent to ISO Class 10.9 for structural use.
No. Hot-dip galvanizing of Class 12.9 fasteners is explicitly prohibited under ISO 4042 and ASTM F2329 due to extreme hydrogen embrittlement risk at proof loads > 1040 MPa. Only mechanical plating (ASTM B695), geomet, or dacromet coatings are permitted. Zinc electroplating requires post-bake hydrogen relief (190°C, 24h minimum) per ASTM B633.

Industrial Cities We Serve:

  • Ahmedabad
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