How to Identify a Hex Bolt’s Grade
Every hex bolt has markings on its head that tell you its material grade and mechanical properties. Those radial lines, numbers, and letters aren’t decorative — they’re a specification. Knowing how to read them means you can verify the right bolt is in the right application without pulling it and checking a cert.
Quick Reference
- No markings — Grade 2, low-carbon steel (the default hardware store bolt)
- 3 radial lines — Grade 5, medium-carbon quenched & tempered (most common structural bolt)
- 6 radial lines — Grade 8, alloy steel quenched & tempered (high-strength)
- “A325” — Structural bolt, equivalent to Grade 5+ (used in steel construction)
- “A490” — Structural bolt, equivalent to Grade 8+ (highest structural grade)
Detailed Grade Identification Table
The table below shows the head markings, material specifications, and mechanical properties (proof load, tensile strength, yield strength) for US and metric bolt grades.
Are you confused about the modest hex bolt, or are you wondering what all those marks mean? This table will help you identify any hex bolt right on the nuts, and it will also tell you about the material grade and mechanical properties. What more could you ask for from a super boring table?
| Hex Bolt Identification Grade Mark |
Specification | Fastener Description |
Material | Nominal Size Range (in.) |
Mechanical Properties | ||
| Proof Load (psi) |
Yield Strength Min (psi) |
Tensile Strength Min (psi) |
|||||
 No Grade Mark |
SAE J429 Grade 1 |
Bolts, Screws, Studs |
Low or Medium Carbon Steel | 1/4 thru 1-1/2 | 33,000 | 36,000 | 60,000 |
| ASTM A307 Grades A&B |
Low Carbon Steel | 1/4 thru 4 | — | — | |||
| SAE J429 Grade 2 |
Low or Medium Carbon Steel | 1/4 thru 3/4 Over 3/4 to 1-1/2 | 55,000 33,000 |
57,000 36,000 |
74,000 60,000 |
||
No Grade Mark |
SAE J429 Grade 4 |
Studs | Medium Carbon Cold Drawn Steel | 1/4 thru 1-1/2 | — | 100,000 | 115,000 |
B5 |
ASTM A193 Grade B5 |
AISI 501 | 1/4 Thru 4 | — | 80,000 | 100,000 | |
B6 |
ASTM A193 Grade B6 |
AISI 410 | 85,000 | 110,000 | |||
B7 |
ASTM A193 Grade B7 |
AISI 4140, 4142, OR 4105 | 1/4 thru 2-1/2 Over 2-1/2 thru 4 Over 4 thru 7 |
— — — |
105,000 95,000 75,000 |
125,000 115,000 100,000 |
|
B16 |
ASTM A193 Grade B16 |
CrMoVa Alloy Steel | 105,000 95,000 85,000 |
125,000 115,000 100,000 |
|||
B8 |
ASTM A193 Grade B8 |
AISI 304 | 1/4 and larger | — | 30,000 | 75,000 | |
B8C |
ASTM A193 Grade B8C |
AISI 347 | |||||
B8M |
ASTM A193 Grade B8M |
AISI 316 | |||||
B8T |
ASTM A193 Grade B8T |
Bolts, Screws, Studs for High-Temperature Service |
AISI 321 | 1/4 and larger | — | 30,000 | 75,000 |
B8 |
ASTM A193 Grade B8 |
AISI 304 Strain Hardened |
1/4 thr 3/4 Over 3/4 thru 1 Over 1 thru 1-1/4 Over 1-1/4 thru 1-1/2 |
— — — — |
100,000 80,000 65,000 50,000 |
125,000 115,000 105,000 100,000 |
|
B8C |
ASTM A193 Grade B8C |
AISI 347 Strain Hardened |
|||||
B8M |
ASTM A193 Grade B8M |
AISI 316 Strain Hardened |
95,000 80,000 65,000 50,000 |
110,000 100,000 95,000 90,000 |
|||
B8T |
ASTM A193 Grade B8T |
AISI 321 Strain Hardened |
100,000 80,000 65,000 50,000 |
125,000 115,000 105,000 100,000 |
|||
L7 |
ASTM A320 Grade L7 |
Bolts, Screws, Studs for Low-Temperature Service |
AISI 4140, 4142 or 4145 |
1/4 thru 2-1/2 | — | 105,000 | 125,000 |
L7A |
ASTM A320 Grade L7A |
AISI 4037 | |||||
L7B |
ASTM A320 Grade L7B |
AISI 4137 | |||||
L7C |
ASTM A320 Grade LC7 |
AISI 8740 | |||||
L43 |
ASTM A320 Grade L43 |
AISI 4340 | 1/4 thru 4 | — | 105,000 | 125,000 | |
B8 |
ASTM A320 Grade B8 |
Bolts, Screws, Studs for Low-Temperature Service |
AISI 304 | 1/4 and larger | — | 30,000 | 75,000 |
B8C |
ASTM A320 Grade B8C |
AISI 347 | |||||
B8T |
ASTM A320 Grade B8T |
AISI 321 | |||||
B8F |
ASTM A320 Grade B8F |
AISI 303 or 303Se |
|||||
B8M |
ASTM A320 Grade B8M |
AISI 316 | |||||
B8 |
ASTM A320 Grade B8 |
AISI 304 | 1/4 thru 3/4 Over 3/4 thru 1 Over 1 thru 1-1/4 Over 1-1/4 thru 1-1/2 |
— — — — |
100,000 80,000 65,00 50,00 |
100,000 80,000 65,00 50,00 |
|
B8C |
ASTM A320 Grade B8C |
AISI 347 | |||||
B8F |
ASTM A320 Grade B8F |
AISI 303 or 303Se |
|||||
B8M |
ASTM A320 Grade B8M |
AISI 316 | |||||
B8T |
ASTM A320 Grade B8T |
AISI 321 | |||||
 |
SAE J429 Grade 5 |
Bolts, Screws, Studs |
Medium Carbon Steel, Quenched and Tempered | 1/4 thru 1 Over 1 to 1-1/2 |
85,000 74,000 |
92,000 81,000 |
120,000 105,000 |
| ASTM A449 | 1/4 thru 1 Over 1 to 1-1/2 Over 1-1/2 thru 3 |
85,000 74,000 55,000 |
92,000 81,000 58,000 |
120,000 105,000 90,000 |
|||
 |
SAE J429 Grade 5.1 |
Sems | Low or Medium Carbon Steel, Quenched and Tempered | No. 6 thru 3/8 |
85,000 | — | 120,000 |
 |
SAE J429 Grade 5.2 |
Bolts, Screws, Studs |
Low Carbon Martensitic Steel, Quenched and Tempered | 1/4 thru 1 | 85,000 | 92,000 | 120,000 |
A325 |
ASTM A325 Type 1 |
High Strength Structural Bolts |
Medium Carbon Steel, Quenched and Tempered | 1/2 thru 1 1-1/8 thru 1-1/2 |
85,000 74,000 |
92,000 81,000 |
120,000 105,000 |
A325 |
ASTM A325 Type 2 |
Low Carbon Martensitic Steel, Quenched and Tempered | 1/2 thru 1 | 85,000 | 92,000 | 120,000 | |
A325 |
ASTM A325 Type 3 |
Atmospheric Corrosion Resisting Steel, Quenched and Tempered | 1/2 thru 1 1-1/8 thru 1-1/2 |
85,000 74,000 |
92,000 81,000 |
120,000 105,000 |
|
 BB |
ASTM A354 Grade BB |
Bolts, Studs |
Alloy Steel, Quenched and Tempered | 1/4 thru 2-1/2 2-3/4 thru 4 |
80,000 75,000 |
83,000 78,000 |
105,000 100,000 |
 BC |
ASTM A354 Grade BC |
105,000 95,000 |
109,000 99,000 |
125,000 115,000 |
|||
 |
SAE J429 Grade 7 |
Bolts, Screws, |
Medium Carbon Alloy Steel, Quenched and Tempered 4 | 1/4 thru 1-1/2 | 105,000 | 115,000 | 133,000 |
 |
SAE J429 Grade 8 |
Bolts, Screws, Studs |
Medium Carbon Alloy Steel, Quenched and Tempered | 1/4 thru 1-1/2 | 120,000 | 130,000 | 150,000 |
| ASTM A354 Grade BD |
Alloy Steel, Quenched and Tempered 4 | ||||||
No Grade Mark |
SAE J429 Grade 8.1 |
Studs | Medium Carbon Alloy or SAE 1041 Modified Elevated Temperature Drawn Steel | 1/4 thru 1-1/2 | 120,000 | 130,000 | 150,000 |
A490 |
ASTM A490 | High Strength Structural Bolts | Alloy Steel, Quenched and Tempered | 1/2 thru 1-1/2 | 120,000 | 130,000 | 150,000 min 170,000 max |
No Grade Mark |
ISO R898 Class 4.6 |
Bolts, Screws, Studs |
Medium Carbon Steel, Quenched and Tempered | All Sizes thru 1-1/2 |
33,000 | 36,000 | 60,000 |
No Grade Mark |
ISO R898 Class 5.8 |
55,000 | 57,000 | 74,000 | |||
| 8.8 or 88 |
ISO R898 Class 8.8 |
Alloy Steel, Quenched and Tempered | 85,000 | 92,000 | 120,000 | ||
| 10.9 or 109 |
ISO R898 Class 10.9 |
120,000 | 130,000 | 150,000 | |||
Your hex bolt may require a hex nut.