Golden rule: A dimensional standard is not automatically a strength or material grade. Standards such as DIN 931, DIN 933, ISO 4014, ISO 4017, ASME B18.2.1 and IFI-145 mainly identify product geometry. The property/material standard controls the required grade and manufacturer marking, unless the product standard explicitly includes mechanical and marking requirements.
š Illustrated PDF version: Download the Fastener Marking Cheatsheet 2026 (PDF, 4 pages) ā includes visual examples of head and nut marks.
Use this guide for receiving-screening only. The purchase order, applicable edition of the standard, product certificate and lot traceability govern acceptance.
1. Metric carbon and alloy steel ā ISO 898
Bolts, screws and studs ā ISO 898-1
| Typical mark | Meaning | Key receiving check |
|---|---|---|
Maker ID + 4.6 | Property class 4.6 | Check dimensions, thread and certificate separately |
Maker ID + 8.8 | Property class 8.8 | Nominal tensile-strength relationship: 8 Ć 100 = 800 MPa |
Maker ID + 10.9 | Property class 10.9 | Higher-strength quenched-and-tempered class |
Maker ID + 12.9 | Property class 12.9 | Very-high-strength class; application and embrittlement controls matter |
The first number multiplied by 100 gives the nominal tensile-strength level in MPa. The second number is the nominal yield-to-tensile ratio expressed in tenths. This is a decoding relationship, not a substitute for test results.
Nuts ā ISO 898-2
| Typical nut mark | Meaning |
|---|---|
Maker ID + 8 | Nut property class 8 |
Maker ID + 10 | Nut property class 10 |
Maker ID + 12 | Nut property class 12 |
04, 05 etc. | Low-profile/thin-nut class system where applicable |
Do not mark a metric nut 8.8: bolt property classes use two numbers; standard full-height nut classes normally use one class number.
2. Stainless steel ā ISO 3506
| Typical mark | General interpretation |
|---|---|
Maker ID + A2-70 | Austenitic stainless grade family A2, property class 70 |
Maker ID + A4-70 | Austenitic stainless grade family A4, property class 70 |
Maker ID + A4-80 | A4 stainless, property class 80 |
A2 or A4 alone does not prove property class 70 or 80. The complete grade/property-class designation is required where marking applies. The mark identifies a standardized grade family and property class, not the exact heat chemistry or certificate traceability.
3. DIN legacy callouts and current references
| Legacy product callout | Current dimensional reference | Strength/material marking source |
|---|---|---|
| DIN 931, hex bolt, partial thread | DIN EN ISO 4014 | ISO 898-1 or ISO 3506-1 |
| DIN 933, hex screw, full thread | DIN EN ISO 4017 | ISO 898-1 or ISO 3506-1 |
| DIN 934, hex nut | DIN EN ISO 4032 or DIN EN ISO 8673 | ISO 898-2 or ISO 3506-2 |
| DIN 6914 structural HV bolt | DIN EN 14399-4 | EN 14399 assembly/system marking |
Procurement rule: DIN 933 A4-80 is meaningful because DIN/ISO identifies the geometry and A4-80 identifies the stainless grade/property class. DIN 933 by itself does not identify strength or stainless grade.
4. EN 14399 preloaded structural assemblies
| Component | Typical System HR mark |
|---|---|
| Bolt | Maker ID + 8.8 HR or specified class/system mark |
| Nut | Maker ID + 8 HR |
| Washer | Required manufacturer/system identification under the applicable part |
HR and HV are different assembly systems. Do not mix bolts, nuts and washers from different systems or unlinked manufacturing lots merely because dimensions appear compatible.
5. SAE inch-series bolts and screws ā SAE J429
| Grade | Common visual grade identifier | Important caution |
|---|---|---|
| Grade 2 | No radial grade lines | Can resemble ungraded, commercial or exempt fasteners |
| Grade 5 | Three radial lines | Similar visual family can occur under ASTM A449 in applicable ranges |
| Grade 8 | Six radial lines | Similar visual family can occur under ASTM A354 Grade BD |
A manufacturer identification is separate from the radial grade identifier. Never identify the governing standard from radial lines alone.
6. SAE inch-series steel nuts ā SAE J995
| Nut grade | Common grade identifier |
|---|---|
| Grade 5 | Two circumferential arcs/lines, 120Ā° apart |
| Grade 8 | Two circumferential arcs/lines, 60Ā° apart |
The nut mechanical standard is SAE J995, not SAE J429.
Correct stack for a 5/8-11 UNC Grade 8 serrated flange nut
- Geometry/serration: IFI-145 or the customer drawing.
- Thread: 5/8-11 UNC-2B.
- Mechanical properties: SAE J995 Grade 8.
- Mark: manufacturer ID plus the J995 Grade 8 identifier.
- Finish: state
plain,plain/oiled, plating or coating separately. - Packing: state maximum carton mass separately.
ASME B18.16.4 is specifically a 90,000 psi serrated flange locknut product standard. It should not be treated as a generic dimensional reference for a SAE J995 Grade 8 product.
7. ASTM structural bolts and nuts
ASTM F3125/F3125M structural bolts
| Product/grade | Typical mandatory grade symbol |
|---|---|
| Heavy-hex Grade A325 Type 1 | A325 plus maker ID |
| Heavy-hex Grade A325 Type 3 | Underlined A325 plus maker ID |
| Heavy-hex Grade A490 Type 1 | A490 plus maker ID |
| Heavy-hex Grade A490 Type 3 | Underlined A490 plus maker ID |
| Twist-off Grade F1852 | A325TC plus maker ID |
| Twist-off Grade F2280 | A490TC plus maker ID |
| Grade 144 structural assembly | 144/applicable assembly mark plus maker ID |
ASTM A563/A563M structural nuts
Common grade symbols include C, C3, D, DH and DH3, with the applicable maker identification. Type 3/weathering designations use the specified distinguishing treatment; do not infer Type 3 from colour or surface appearance.
8. ASTM pressure-service bolting ā A193/A194
| Product standard | Common examples of grade marks |
|---|---|
| ASTM A193/A193M bolts and studs | B7, B7M, B16, B8, B8M, with maker identification and any required class/condition marks |
| ASTM A194/A194M nuts | 2H, 2HM, 7, 7M, 8, 8M, with maker identification and any required class/condition marks |
The M in grades such as B7M, B8M, 2HM or 7M is part of the ASTM grade designation. It does not mean that the thread is metric. The order must separately state inch or metric thread requirements and whether the ASTM M specification designation applies.
9. Other common ASTM systems
| Product | Typical marking concept | Procurement caution |
|---|---|---|
| ASTM F1554 anchor rods | Grade 36, 55 or 105 when permanent marking is ordered | Permanent maker/grade identification is a supplementary requirement; call it up explicitly |
| ASTM F593 stainless bolts | Examples: F593C, F593D, F593G, F593H | Letter encodes alloy group, condition and applicable diameter range |
| ASTM F594 stainless nuts | Corresponding F594C/D/G/H, as applicable | Match alloy group and proof strength to the bolt |
| ASTM A307 general-purpose bolts | Grade B commonly uses B; Grade A may be unmarked/exempt | Absence of radial lines does not establish A307 Grade A |
10. AS/NZS structural bolt assemblies
For Australian structural work, treat AS/NZS 1252.1 bolt/nut/washer sets as traceable functional assemblies. The Australian Steel Institute identifies EN 14399-3 System HR property class 8.8 as the nominated alternative, with additional assembly types only where expressly specified. Do not interchange AS/NZS components with EN 14399 HR or HV components within one assembly.
Receiving checks should include manufacturer mark, property class/system mark, package and lot identification, SDoC/DoP where applicable, EN 10204 3.1 documentation where specified, and any Australian verification requirement.
11. What a head or nut mark does not prove
A correct-looking mark does not by itself establish:
- thread series, pitch, tolerance class or left-hand thread;
- coating or finish;
- exact material heat chemistry;
- heat/lot traceability;
- dimensional conformity;
- full mechanical-test compliance;
- corrosion, temperature, fatigue or hydrogen-embrittlement suitability;
- authenticity of the stamp.
12. Five-step receiving check
- Read the PO: identify geometry, thread, grade, finish, standard edition and certification requirements.
- Identify every mark: maker, property/grade class, structural system, type/class and special symbols.
- Match the package: connect the fastener to its packing label, heat/lot/batch and trace number.
- Review documents: MTR, EN 10204 3.1 certificate, SDoC, DoP or test report as required.
- Escalate ambiguity: quarantine mixed, illegible, mismarked or undocumented product; do not infer grade from appearance.
Primary references checked
- ISO 898-1:2013 with Corrigendum 1 and ISO 898-2:2022.
- ISO 3506-1:2020 and ISO 3506-2:2020.
- DIN Media status and replacement records for DIN 931, 933, 934 and 6914.
- SAE J429 MAY2014 and SAE J995 JUL2017.
- ASTM F3125/F3125M-25a, ASTM A563/A563M, ASTM A193/A193M-26, ASTM A194/A194M-26, ASTM F593-24, ASTM F594-24 and ASTM F1554-20.
- RCSC 2020 Specification for Structural Joints Using High-Strength Bolts.
- AS/NZS 1252.1:2016 and Australian Steel Institute TN001/TN016.
- ASME B18.16.4-2008 and ASME B18.6.4/B18.6.3 status information.
Standards are copyrighted and may be revised. The purchased/current standard text and the contractual purchase specification govern acceptance.