Most Common Bolt Head Markings
The head markings you will actually see, grouped by standard. Lines and numbers identify the grade or class; letters or a logo off to the side identify the manufacturer.
Common head markings
| Marking | What it is | Standard | Note |
|---|---|---|---|
| No mark (maker ID only) | Grade 2, or unknown | SAE J429 | Unmarked is not proven Grade 2 |
| 3 radial lines, 120 deg | Grade 5 (also A449) | SAE J429 / ASTM A449 | Check maker and certs |
| 6 radial lines, 60 deg | Grade 8 | SAE J429 | |
| 8.8 | Property class 8.8 | ISO 898-1 | Nominal 800 MPa |
| 10.9 | Property class 10.9 | ISO 898-1 | Nominal 1000 MPa |
| 12.9 | Property class 12.9 | ISO 898-1 | Usually socket heads |
| A325 (heavy hex) | Structural bolt | ASTM F3125 | Underlined = Type 3 |
| A490 (heavy hex) | Structural bolt | ASTM F3125 | No plating allowed |
| 307A / 307B | A307 Grade A / B, when marked | ASTM A307 | Often maker ID only |
| BC / BD | A354 Grade BC / BD | ASTM A354 | |
| B7 (on stud end) | A193 B7 alloy stud | ASTM A193 | Pair with A194 2H |
| 18-8 / 304 / 316 | Stainless alloy family | (alloy name) | Not a strength grade |
| A2-70 / A4-70 / A4-80 | Stainless group + class | ISO 3506 | A2 = 304 type, A4 = 316 type |
These tables carry the same figures as the printed sheet below.
The printed sheet
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Text version of this sheet
Field identification · head markings by standard family
What it is
FIELD IDENTIFICATION
The head markings you will actually see, grouped by standard. Lines and numbers identify the grade
or class; letters or a logo off to the side identify the manufacturer.
MFG
MFG
MFG
MFG
MFG
8.8
10.9
Gr 2
Gr 5
Gr 8
8.8
10.9
Lines and class numbers are the grade; MFG is
the maker
Common head markings
Marking
What it is
Standard
Note
No mark (maker ID only)
Grade 2, or unknown
SAE J429
Unmarked is not proven Grade 2
3 radial lines, 120 deg
Grade 5 (also A449)
SAE J429 / ASTM A449
Check maker and certs
6 radial lines, 60 deg
Grade 8
SAE J429
8.8
Property class 8.8
ISO 898-1
Nominal 800 MPa
10.9
Property class 10.9
ISO 898-1
Nominal 1000 MPa
12.9
Property class 12.9
ISO 898-1
Usually socket heads
A325 (heavy hex)
Structural bolt
ASTM F3125
Underlined = Type 3
A490 (heavy hex)
Structural bolt
ASTM F3125
No plating allowed
307A / 307B
A307 Grade A / B, when marked
ASTM A307
Often maker ID only
BC / BD
A354 Grade BC / BD
ASTM A354
B7 (on stud end)
A193 B7 alloy stud
ASTM A193
Pair with A194 2H
18-8 / 304 / 316
Stainless alloy family
(alloy name)
Not a strength grade
A2-70 / A4-70 / A4-80
Stainless group + class
ISO 3506
A2 = 304 type, A4 = 316 type
Key points
A head with a grade mark and no maker mark is incomplete and suspect.
Markings identify material grade, not which product standard the part was made to.
Governing standards: SAE J429 (2014); ISO 898-1:2013; ASTM F3125/F3125M-26; ASTM A307-21; ASTM A354-26; ASTM A193/A193M-24; ISO 3506-1/-2:2020. Editions shown
are the latest confirmed as of September 2026. The drawing and the governing standard always take precedence over this sheet.
torquing any fastener. Verify the current governing standard, project documents, OEM requirements, size, thread, coating and lot certification. To the fullest extent permitted by law, The Fastener App disclaims liability
arising from reliance on this reference.
Fastener Guide reference FG-5BC336 · thefastenerapp.com/fastener-guide/technical-reference/most-common-bolt-head-markings · © The Fastener App. Reference only — verify the current governing standard, drawing and manufacturer data before specifying or installing.
