Grades of Bolts - Bolt Grade Markings & Bolt Strength Chart

This chart helps to identify the grades of bolts using the identification marks on the bolt's head along with the strength and hardness of common grade bolts. Please note the bolt heads may also include the manufacturer's identification stamp, especially with high strength bolts.

Bolt Grade Markings & Strength Chart - Inch Steel Bolts

Head Marking

Bolt Grade / Specification

Material

Nominal Size (Inch)

Proof Load psi

Tensile Strength Min psi

Yield Strength Min psi

Rockwell Hardness Min/Max

SAE J429 - Grade 1 Head Markings

Grade 1 - SAE J429

Bolts, Screws and Studs 

Low or medium carbon steel  1/4" - 1-1/2" 33,000  60,000  36,000 B70 / B100
SAE J429 - Grade 2 Head Markings

Grade 2 - SAE J429

Bolts, Screws and Studs

 Low or medium carbon steel

1/4" - 3/4" 

>3/4" - 1-1/2"

55,000

33,000

74,000

60,000 

57,000

36,000 

B80 / B100

B70 / B100

 Grade 5 Bolt Markings

Grade 5 - SAE J429

Bolts, Screws and Studs

Medium carbon steel or carbon steel with additives, quenched and tempered 

1/4" - 1"

>1" - 1-1/2"

85,000

74,000

120,000

105,000

92,000

81,000

C25 / C34

C19 / C30

 Grade 5.1 Bolt Markings

 Grade 5.1 - SAE J429

Sems

Low or medium carbon steel, quenched and tempered 

No. 4 - 5/8"

85,000

120,000

92,000

C25 / C40

 Grade 5.2 Bolt Markings

 Grade 5.2 - SAE J429

Bolts, Screws and Studs

 Low carbon Boron steel, quenched and tempered

1/4" - 1"

85,000 

120,000

92,000

C26 / C36

 Grade 8 Bolt Markings

 Grade 8 - SAE J429

Bolts and Screws

Medium carbon / alloy steel with additives, quenched and tempered 

1/4" - 1-1/2"

120,000 

150,000

130,000

C33 / C39 

 Grade 8.2 Bolt Markings

  Grade 8.2 - SAE J429

Bolts and Screws

 Low carbon Boron steel, quenched and tempered

1/4" - 1"

120,000

150,000

130,000

C33 / C39 

L9 Bolt Markings 

L9 - Grade 9

Bolts, Nuts and Washers

 Hight strength alloy steel

1/4" - 1-1/2"

145,000

180,000

155,000

C38 / C42

 307A Bolt Markings

 ASTM A307 Grade A

Bolts, Screws and Studs (General Engineering)

Low or medium carbon steel

1/4" - 4"

33,000

60,000

36,000

B69 / B100

307B Bolt Markings

ASTM A307 Grade B

Bolts, Screws and Studs (Flanged Joints)

 Low or medium carbon steel

1/4" - 4"

33,000

60,000

36,000 

B69 / B95

A325 Bolt Markings

ASTM A325 Type 1

High strength structural bolts

 Medium carbon steel, quenched and tempered

1/2" - 1"

1-1/8" - 1-1/2"

85,000

74,000

120,000

105,000

92,000

81,000

C24 / C35

C19 / C31

A325 Type 2 Bolt Markings

ASTM A325 Type 2

High strength structural bolts

Low carbon Martensitic steel, quenched and tempered 

1/2" - 1"

1-1/8" - 1-1/2"

85,000

74,000

120,000

105,000

92,000

81,000

C24 / C35

C19 / C31

A325 Type 3 Bolt Markings

ASTM A325 Type 3

High strength structural bolts

Atmospheric corrosion-resistant steel, quenched and tempered 

1/2" - 1"

1-1/8" - 1-1/2"

85,000

74,000

120,000

105,000

92,000

81,000

C24 / C35

C19 / C31

ASTM A354 Grade BB Bolt Markings

ASTM A354 Grade BB

Bolts and studs

 Alloy steel, quenched and tempered

1/4" - 2-1/2"

> 2-1/2" - 4"

80,000

75,000

105,000

100,000

83,000

78,000

 C26 / C36

C22 / C33

ASTM A354 Grade BC Bolt Markings

ASTM A354 Grade BC

Bolts and studs

Alloy steel, quenched and tempered 

1/4" - 2-1/2"

> 2-1/2" - 4"

105,000

95,000

125,000

115,000

109,000

99,000

C26 / C36

C22 / C33

ASTM A354 Grade BD Bolt Markings

ASTM A354 Grade BD

Bolts, screws and studs

 Alloy steel, quenched and tempered

1/4" - 2-1/2"

> 2-1/2" - 4"

120,000

105,000

150,000

140,000

130,000

120,000

C33 / C39

C31 / C39

ASTM A449 Type 1 Bolt Markings

ASTM A449 Type 1

Bolts, screws and studs

 Medium carbon steel, quenched and tempered

1/4" - 1"

>1 - 1-1/2"

85,000

74,000

120,000

105,000

81,000

58,000

C25 / C34

C19 / C30

ASTM A449 Type 2 Bolt Markings

ASTM A449 Type 2

Bolts, Screws and studs

Low carbon Martensitic steel, quenched and tempered 

1/4" - 1"

85,000 

120,000

58,000

 C25 / C34

 ASTM A490 Type 1 Bolt Markings

ASTM A490 Type 1

High strength structural bolts

 Medium carbon alloy steel, quenched and tempered

1/2" - 1-1/2"

120,000

150,000 min

170,000 max

130,000

 C33 / C38

ASTM A490 Type 2 Bolt Markings

ASTM A490 Type 2

High strength structural bolts

Low carbon Martensitic steel, quenched and tempered 

1/2" - 1"

120,000 

150,000 min

170,000 max

130,000

 C33 / C38

 ASTM A490 Type 3 Bolt Markings

ASTM A490 Type 3

High strength structural bolts

Atmospheric corrosion-resistant steel, quenched and tempered

1/2" - 1-1/2"

120,000

150,000 min

170,000 max

130,000

 C33 / C38

Note: Manufacturer's identification mark are also stamped when applicable.

 

Bolt Grade Markings & Strength Chart - Metric Steel Bolts

Head Marking

Grade/Specification

Material

Proof Load (MPa) 

Tensile Strength min (MPa)

Yield Strength Min (MPa)

Hardness Min/Max

Class 4.6 Bolt Markings

Class 4.6

Low or medium carbon steel 220 400 (58,000 psi) 240 HRB-67 / HRB-95
Class 5.8 Bolt Markings

Class 5.8

 Low or medium carbon steel, quenched and tempered

380

520 (75,000 psi)

420

HRB-82 / HRB-95

Class 8.8 Bolt Markings

Class 8.8

Medium carbon steel, quenched and tempered 

600 

830 (120,000 psi)

640

HRC-22 / HRC-34

Class 10.9 Bolt Markings

Class 10.9

Alloy steel, quenched and tempered

830

1040 (150,000 psi)

940

HRC-32 / HRC-39

Class 12.9 Bolt Markings

Class 12.9

 Alloy steel, quenched and tempered

970

1220 (176,000 psi)

1220

HRC-39 / HRC-44

Usually stamped A-2 or A-4 

A2 & A4 Stainless

 

 Steel alloy with chromium and nickel

N/A

500 Min

700 Typical

210 Min

450 Typical

 

Note: Manufacturer's identification mark are also stamped when applicable.

 

Tensile Strength: The resistance of a material to breaking under tension

Yield Strength: The stress at which a specific amount of deformation is produced

Proof Load: An axial tensile load which the product must stand without evidence of any permanent set.

 

Additional Resources

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Download Bolt Grade Marking Chart PDF

Bolt Grade Marking Chart
 
 

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