Carbon Steel Bolt — Factory Direct Supplier | Huaxia-Steel
Carbon steel bolts are the workhorse fastener for structural connections, flange joints, machinery assembly and general construction. Choosing the correct ASTM grade, mechanical class, and coating at the design stage prevents joint loosening, fatigue failure, and costly rework. The four most common grades — ASTM A307 Gr.A / Gr.B, A325, A490 and A193 B7 — cover 90% of all structural and pressure-vessel bolting requirements.
Huaxia Steel supplies factory-direct carbon steel bolts in standard metric and imperial sizes, with full MTC 3.1 / 3.2 certification, hot-dip galvanizing, zinc plating, PTFE / Xylan coating, and NACE MR0175 sour-service qualification. All bolts are traceable to the original bar heat.
1. Product Overview
Carbon steel bolts are externally threaded fasteners with a head on one end and a partially or fully threaded shank. They are used in:
- Structural steel connections (beams, columns, bracing, base plates)
- Flange joints for piping and pressure vessels
- Heavy machinery and equipment mounting
- Bridge construction and repair
- Wind tower and transmission tower assembly
- General construction and steel fabrication
Bolts are typically supplied with matching nuts (ASTM A563) and washers (ASTM F436). For high-strength structural bolting, the complete assembly is usually specified per ASTM F3125.
2. Grade Comparison and Mechanical Properties
The table below compares the most common bolt grades:
| Grade | Min Tensile (ksi) | Min Yield (ksi) | Typical Use |
|---|---|---|---|
| ASTM A307 Gr.A | 60 | 30 | General-purpose low-strength bolting |
| ASTM A307 Gr.B | 60–100 | 30–57 | General-purpose, higher tensile |
| ASTM A325 (now F3125 Gr.A325) | 120 | 92 | High-strength structural |
| ASTM A490 (now F3125 Gr.A490) | 150–170 | 130 | Highest-strength structural |
| ASTM A193 B7 | 125 | 105 | High-temperature pressure service |
| ASTM A193 B7M | 100 | 80 | Sour service (NACE MR0175) |
| ASTM A320 L7 | 125 | 105 | Low-temperature service to −150°F |
| ISO 898-1 Class 8.8 | 116 | 92 | Metric general-purpose high-strength |
| ISO 898-1 Class 10.9 | 150 | 130 | Metric highest-strength |
3. Available Sizes
Carbon steel bolts are available in the following standard sizes:
| Standard | Diameter Range | Length Range |
|---|---|---|
| Imperial (ASME B18.2.1) | 1/4 inch to 4 inch | 1/2 inch to 24 inch |
| Metric (ISO 4014 / 4017) | M6 to M64 | 20 mm to 600 mm |
| Heavy hex (ASME B18.2.1) | 1/2 inch to 4 inch | 1-1/2 inch to 24 inch |
| Stud bolt (ASME B18.2.1 / B16.5) | 1/4 inch to 4 inch | Up to 36 inch |
Common head styles include hex head, heavy hex head, countersunk, carriage, eye bolt, and U-bolt. Threading can be UNC (coarse), UNF (fine), or metric coarse / fine per ISO 261.
4. Head Styles and Configurations
| Head Style | Standard | Typical Application |
|---|---|---|
| Hex head | ASME B18.2.1 / DIN 933 | General purpose |
| Heavy hex head | ASME B18.2.1 / ASTM F3125 | High-strength structural |
| Socket head cap | ASME B18.3 / ISO 4762 | Precision machinery |
| Countersunk | ASME B18.3 / ISO 10642 | Flush surface requirements |
| Carriage bolt | ASME B18.5 | Wood-to-metal |
| Eye bolt | ASME B18.15 | Lifting, rigging |
| U-bolt | ASME B18.31.5 | Pipe support, conduit |
| Stud bolt | ASME B18.2.1 / B16.5 stud | Flanged joints |
5. Coating and Finishing Options
Carbon steel bolts are available with the following coatings:
- Plain (black) — as-forged / as-rolled surface, suitable for indoor dry service
- Hot-dip galvanizing — per ASTM A153 / ISO 1461, 50–100 µm zinc coating, ideal for outdoor atmospheric service
- Electro-zinc plating — per ASTM B633, 5–25 µm zinc coating, indoor / mild atmosphere
- Mechanical galvanizing — per ASTM B695, 25–75 µm zinc, no hydrogen embrittlement
- PTFE / Xylan / Teflon coating — 15–30 µm fluoropolymer, corrosion + low friction
- Dacromet / Geomet — zinc flake coating, no hydrogen embrittlement
- Cadmium plating — for marine / aerospace (restricted due to toxicity)
For sour service (NACE MR0175), specify cadmium-plated, PTFE-coated, or zinc-flake-coated bolts. Hot-dip galvanizing and acid-pickled bolts can introduce hydrogen embrittlement risk in high-strength grades above 10.9 / Grade 8.
6. Manufacturing Standards
Carbon steel bolts are manufactured per the following standards:
- ASTM A307 — Carbon steel bolts and studs, 60,000 psi tensile strength
- ASTM A325 — High-strength bolts for structural steel joints (now F3125 Gr.A325)
- ASTM A490 — Highest-strength structural bolts (now F3125 Gr.A490)
- ASTM A193 — Alloy steel and stainless steel bolting for high-temperature service
- ASTM A320 — Alloy steel bolting for low-temperature service
- ASTM F3125 — Standard specification for high-strength structural bolts
- ISO 898-1 — Mechanical properties of fasteners made of carbon steel and alloy steel
- ASME B18.2.1 — Square and hex bolts and screws
- DIN 933 — Hexagon head bolts, product grade A and B
7. Applications
Carbon steel bolts are used in:
- Structural steel — building frames, bridges, transmission towers, wind towers
- Pressure vessel flanges — per ASME B16.5 stud bolt sizing
- Piping flanges — per ASME B16.5 / B16.47 stud bolt selection
- Oil and gas — wellhead, christmas tree, manifold bolting
- Refinery and petrochemical — heat exchanger, reactor, column bolting
- Power plant — turbine, generator, boiler bolting
- Heavy machinery — mining, cement, steel mill equipment
- Shipbuilding — hull, deck, superstructure
8. Quality Assurance
Every batch of carbon steel bolts from Huaxia Steel is supplied with:
- EN 10204 Type 3.1 / 3.2 mill test certificate
- Heat analysis with actual C, Mn, P, S, Si values (and Cr, Mo, B for alloy grades)
- Mechanical test per ASTM F606 / ISO 898-1 (proof load, tensile strength, hardness)
- Charpy V-notch test for low-temperature grades (A320 L7)
- Hardness test per NACE MR0175 for sour service
- Coating thickness test per ASTM B633 / A153
- Dimensional inspection per ASME B18.2.1 / ISO 4014
- Thread gauge verification per ASME B1.1 / ISO 261
9. Packaging and Shipping
Standard packaging for carbon steel bolts:
- Small bolts (1/4 to 5/8 inch): cardboard boxes, 50–500 pieces per box
- Medium bolts (3/4 to 1-1/2 inch): wooden crates, 25–100 pieces per crate
- Large bolts (1-3/4 to 4 inch): wooden pallets with shrink-wrap
- Bulk packaging in steel drums for high-volume orders
- All bolts packed in plastic bags with desiccant and VCI paper for corrosion protection
- Marking: manufacturer, grade, diameter, length, standard, heat number, project number
- 20 ft or 40 ft container export packaging available
Standard lead time is 7–15 days for stocked sizes and 20–45 days for mill-run orders. Hot-dip galvanizing adds 10–15 days to lead time.
10. Bolt Selection Tips
Choosing the right bolt for the application avoids premature failure and costly rework:
- Structural connections — use A325 for bearing-type or slip-critical connections; use A490 for higher strength requirements; verify WPS / PQR per AWS D1.1
- Flanged joints — select stud bolt length per ASME B16.5 Table 6; verify nut and washer per ASME B16.5 and matching grade
- High-temperature service — use A193 B7 above 400°F; use B16 for higher temperature up to 1200°F; use B8 (stainless) above 1200°F
- Low-temperature service — use A320 L7 below −50°F; use L7M for reduced hardness in sour service
- Sour service (H2S) — specify NACE MR0175 with hardness limit 22 HRC; use cadmium plating or PTFE coating to avoid hydrogen embrittlement
- Galvanic corrosion — match the bolt material to the connected material; avoid direct contact between stainless steel bolts and carbon steel structural members in corrosive environments
For critical joints, request torque-tension verification at installation. Over-tightening causes thread stripping; under-tightening causes joint loosening. Verify with torque wrench per ASME PCC-1.
11. Cost and Lead Time Considerations
Carbon steel bolt pricing depends on the grade, diameter, length, quantity and coating. As a rule of thumb:
- A307 Gr.A is the baseline reference price for general-purpose low-strength bolting
- A307 Gr.B adds 5–10% over Gr.A for higher tensile strength
- A325 (F3125 Gr.A325) adds 30–50% over A307 for high-strength structural
- A490 (F3125 Gr.A490) adds 50–80% over A307 for highest-strength structural
- A193 B7 adds 40–60% over A307 for high-temperature pressure service
- A320 L7 adds 60–90% over A307 for low-temperature service
- ISO Class 8.8 is roughly equivalent to A325 in metric pricing
- ISO Class 10.9 is roughly equivalent to A490 in metric pricing
- Hot-dip galvanizing adds 20–30% over plain for the coating process
- NACE MR0175 adds 5–10% for hardness control and documentation
Standard lead time is 7–15 days for stocked sizes and 20–45 days for mill-run orders. Hot-dip galvanizing adds 10–15 days to lead time. PTFE coating adds 5–10 days. High-strength grades above A325 or metric Class 10.9 require longer heat-treatment cycles, adding 5–10 days.
Need carbon steel bolts for your project? Huaxia Steel supplies A307, A325, A490, A193 B7 and A320 L7 bolts in all standard sizes, with full MTC 3.1 / 3.2 and SGS / BV / TUV witnessed inspection. Email [email protected] with your grade, diameter, length, quantity and coating requirement, and we will respond with a mill-direct quotation within 24 hours.
