Fastener Standards & Grades: Cross-Reference for Export Buyers
A quotation is only comparable when the standard is clear. This page cross-references the metric and inch standards most often used on infrastructure projects, explains property classes, and lists the coating specifications a buyer can put on the drawing.
Standards covered on this page
Metric standards
DIN, ISO, GB/T and EN equivalents for hex bolts, nuts, washers and threaded rod, with the differences explained.
Inch and US standards
ASTM A325 / A490, SAE J429 and ANSI/ASME B18.2.1 bolt dimensions for US-facing projects.
Quality & inspection →Property classes
8.8, 10.9, 12.9, A2-70, A4-80 and ASTM Grade 5/8 explained with typical materials and applications.
Why a standard reference matters in a quotation
Two bolts can look identical and still not be interchangeable. The standard fixes the dimensions; the property class fixes the strength; the coating specification fixes the corrosion resistance and the friction coefficient. When a quotation only says "hex bolt M20", three different parts can be quoted. Putting the standard, class and coating on the drawing is the simplest way to get a comparable price and a part that fits.
Metric hex bolt cross-reference
| Type | DIN | ISO / EN | GB/T | Note |
|---|---|---|---|---|
| Hex bolt with partial thread | DIN 931 | ISO 4014, EN 14399-3 (structural) | GB/T 5782 | Thread length differs by diameter and length; confirm the standard |
| Hex bolt with full thread | DIN 933 | ISO 4017 | GB/T 5783 | Not a replacement for BS EN 14399-3 in preloaded structural joints |
| Hex nut | DIN 934 | ISO 4032, EN 14399-4 | GB/T 6170 | Nominal heights differ between DIN and ISO series |
| Plain washer | DIN 125 | ISO 7089 | GB/T 97.1 | Check thickness and diameter series for the joint design |
| Spring washer | DIN 127 | — | GB/T 93 | Used for anti-loosening in general connections |
| Threaded rod | DIN 975 | ISO 4762 / other | GB/T 15389 | Jointing rod standards vary; confirm the number |
Inch and US fastener standards
| Type | Standard | Typical grade | Where it is used |
|---|---|---|---|
| Heavy hex structural bolt | ASTM A325 / A490, ASME B18.2.6 | A325 Type 1 / Type 3; A490 | Structural steel connections in the US |
| Hex cap screw | ASME B18.2.1, SAE J429 | Grade 2, 5, 8 | General machinery and steelwork |
| Hex nut | ASME B18.2.2 | Grade 5, Grade 8, A194 2H | Matched to the bolt grade |
| Washer | ASME B18.22.1 | Hardened / plain | Preloaded structural joints use hardened washers |
Do not mix imperial thread series: UNC and UNF are not interchangeable, and 1/2-13 UNC is not the same part as M12. State the thread series and TPI on the enquiry.
Property classes and typical materials
| Class / grade | Nominal tensile strength | Typical material | Typical use |
|---|---|---|---|
| 8.8 | 800 MPa | Medium carbon steel, quenched and tempered | General steelwork, machine frames, supports |
| 10.9 | 1000 MPa | Alloy steel (e.g. 35CrMo / 40Cr) | Structural connections, segment lifting, heavy equipment |
| 12.9 | 1200 MPa | Alloy steel, controlled heat treatment | High-strength machinery joints |
| A2-70 / A4-70 / A4-80 | 700 / 800 MPa | Stainless steel 304 / 316 | Facades, coastal and chemically exposed areas |
| SAE Grade 5 / 8 | 120 000 / 150 000 psi | Medium carbon / alloy steel | US machinery and automotive-type joints |
Coating specifications often called out on drawings
| Coating | Reference standard | Typical thickness | Points to confirm |
|---|---|---|---|
| Hot-dip galvanizing | ISO 1461, ASTM A153, GB/T 13912 | ≥ 45 µm (varies by thickness) | Thread allowance after galvanizing, re-tapping, handling damage |
| Zinc flake / Dacromet | ISO 10683, ASTM F1941 | 8–15 µm | Friction coefficient, torque, salt-spray hours |
| Electroplating | ISO 4042, ASTM F1941 | 5–15 µm | Hydrogen embrittlement relief for 10.9 and above |
| Phosphating | ISO 9717 | 3–10 µm | Oil or topcoat follow-up, storage protection |
| Mechanical zinc coating | ISO 12683 | 8–12 µm | Thread allowance and torque coefficient |
For high-strength bolts, confirm whether the coating process can introduce hydrogen. Electroplated 10.9 and 12.9 parts normally require a bake-out after plating; hot-dip galvanizing and zinc flake do not involve the same acid pickling step.
Inspection documents matched to the standard
- Material certificate: heat number, chemical composition and mechanical properties to the governing standard.
- Dimensional report: thread gauge, length, head dimensions and, for bent parts, the bend radius.
- Mechanical test: tensile, proof load and hardness, as required by the class or the project specification.
- Coating report: coating thickness, adhesion and salt-spray hours to the specified method.
- Third-party testing: arranged where the contract requires an accredited laboratory report.
What to state on the drawing or enquiry
| Item | Example |
|---|---|
| Standard | ISO 4017 / DIN 933 / GB/T 5783; or ASTM A325 |
| Thread | M20 x 2.5; or 3/4-10 UNC |
| Length | 80 mm under head; state whether length includes the head |
| Property class / grade | 10.9; or SAE Grade 8 |
| Coating | Hot-dip galvanized to ISO 1461; or zinc flake to ISO 10683 |
| Inspection | Material certificate + salt-spray 480 h; or third-party tensile test |
Related pages
- High-strength bolts — 8.8 / 10.9 production and inspection
- Segment bolts — curved bolts to drawing for tunnel linings
- Nuts & washers — matched nut and washer supply
- Quality & inspection — test reports and third-party checks
- Contact — send a drawing for quotation
Send a drawing or specification for quotation
Include the interface, material, grade, coating, quantity and delivery stage. We will confirm feasibility, tooling where needed, documents and lead time before quoting.
Tel / WhatsApp / WeChat: +86 185 3100 8199
Email: sales@huilang.top
Related applications
- Metro & shield tunnel fasteners
- Road & rail sound barrier fasteners
- Curtain wall & facade fasteners
FAQ
- Is DIN 933 the same as ISO 4017?
- The dimensional series is closely related, but the two standards are not identical in every detail, and project specifications sometimes add requirements. State both if the drawing is based on DIN and the project asks for ISO.
- Can 8.8 bolts be used instead of 10.9?
- Only if the joint design allows it. The two classes differ in tensile strength, proof load and often in material and heat treatment, so substitution should be confirmed by the designer rather than decided at the factory.
- What is the difference between A2-70 and A4-80?
- A2 is 304-type stainless with 700 MPa nominal tensile strength; A4 is 316-type stainless with 70 or 80 class strength. A4 is preferred for coastal and chloride exposure.
- Which coating should be specified for outdoor steelwork?
- Hot-dip galvanizing to ISO 1461 or ASTM A153 is the common choice. Zinc-flake coatings are used where a controlled friction coefficient matters. For coastal or de-icing-salt exposure, confirm the salt-spray duration and consider stainless or a duplex system.
- Do you supply material certificates and test reports?
- Yes. Material certificates, dimensional and coating inspection records and packing lists with heat or batch identity are supplied. Third-party tensile, hardness, salt-spray or weld testing can be arranged where the contract requires it.
- Can you produce to a project specification instead of a published standard?
- Yes. Many infrastructure projects use a project specification that adds requirements on top of a standard. Send the specification and the drawing so the material, heat treatment, coating and inspection plan can be confirmed before quoting.