Mechanical decoder
Bolt Grade Decoder
Decode common metric property classes, SAE grades, stainless classes, and ASTM bolt markings.
Inputs
Results
- Decoded result
- Waiting for input
- Confidence
- Waiting for input
Segment breakdown
Matched fields
Use the decoder above to read a bolt head marking. Enter the marking exactly as printed: metric property class, SAE grade, stainless class, or ASTM designation. The tool separates the marking system from the strength meaning.
Reference Table
| Input | Decoded result |
|---|---|
| 8.8 | Metric property class 8.8: medium carbon steel, quenched and tempered |
| 10.9 | Metric property class 10.9: high-strength alloy steel |
| Grade 8 | SAE Grade 8: high-strength inch-series bolt (radial lines on head) |
| A2-70 | Stainless class: A2 austenitic steel, 700 MPa tensile |
Code Structure
| System | How to read |
|---|---|
| Metric (8.8, 10.9) | Digits before the dot relate to tensile strength; after the dot to yield ratio. |
| SAE (Grade 5, Grade 8) | Inch-series grades; head radial lines encode the grade. |
| Stainless (A2-70) | Steel group plus tensile strength class in MPa divided by 10. |
| ASTM (A325, A490) | Structural bolt specifications; confirm standard edition. |
How To Decode
- Enter the head marking exactly as printed, including dots, dashes, and grade words.
- Identify the system first — metric, SAE, stainless, or ASTM — before reading strength.
- Verify diameter, thread, length, coating, and the governing standard before any structural or safety use.
Sources And Limits
ISO metric fastener property class conventions, SAE grade markings, ASTM references, and stainless fastener class guides; verified 2026-08-26. The head marking alone never confirms dimensions, preload, or fitness for a structural joint.
Decode logic
- Identify the marking system first: dotted metric classes (8.8), SAE Grade numbers (Grade 8), stainless classes (A2-70), or ASTM designations.
- For metric classes, read the first number as nominal tensile strength in hundreds of MPa and the second as the yield ratio: 8.8 means 800 MPa class with 0.8 ratio.
- For SAE grades, read the grade number as the strength family (head radial lines confirm); for stainless, read the alloy family plus strength class (A2-70 is 700 MPa class).
- Use the decoded marking as a class reading aid only and verify proof load, head marking, coating, and lot traceability against the standard and test report.
FAQs
What do the two 8s in 8.8 mean?
The first 8 is the 800 MPa nominal tensile strength class and the second 8 is the 0.8 yield ratio. Confirm proof load in ISO 898-1 for the exact size.
Is Grade 8 the same as 8.8?
No. Grade 8 is an SAE inch-system grade while 8.8 is an ISO metric property class. They belong to different systems and are not interchangeable.
What does the 70 mean in A2-70?
70 is the 700 MPa tensile strength class in the A2 austenitic stainless family. Corrosion and galling behavior still need the product data sheet.
How do I enter an ASTM A325 marking?
Enter the full visible marking including the ASTM designation. Verify grade, coating, and lot documentation against the standard before structural use.