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Bolt Grade Markings and Strength Chart

Head Markings

Grade or Class

Material

Nominal Size Range
(Inches)

Mechanical Properties

Proof Load (psi)

Minimum Yield Strength (psi)

Minimum Tensile Strength (psi)

American Bolts

No Markings

Grade 2

Low or Medium Carbon Steel

1/4 thru 3/4

55,000

57,000

74,000

Over 3/4 thru 1-1/2

33,000

36,000

60,000


3 Radial Lines

Grade 5

Medium Carbon Steel, Quenched and Tempered

1/4 thru 1

85,000

92,000

120,000

Over 1 thru 1-1/2

74,000

81,000

105,000


6 Radial Lines

Grade 8

Medium Carbon Alloy Steel, Quenched and Tempered

1/4 thru 1-1/2

120,000

130,000

150,000

Stainless markings vary. Most stainless is non-magnetic

18-8 Stainless

Steel alloy with 17-19% Chromium and 8-13% Nickel

1/4 thru 5/8

 

40,000 Min. 80,000 – 90,000 Typical

100,000 – 125,000 Typical

3/4 thru 1

 

40,000 Min. 45,000 – 70,000 Typical

100,000 Typical

Above 1

 

80,000 – 90,000 Typical

Metric Bolts


8.8

Class 8.8

Medium Carbon Steel, Quenched and Tempered

All Sizes thru 1-1/2

85,000

92,000

120,000


10.9

Class 10.9

Alloy Steel, Quenched and Tempered

All Sizes thru 1-1/2

120,000

130,000

150,000

Stainless markings vary. Most stainless is non-magnetic

A-2 Stainless

Steel alloy with 17-19% Chromium and 8-13% Nickel

1/4 thru 5/8

 

40,000 Min. 80,000 – 90,000 Typical

100,000 – 125,000 Typical

3/4 thru 1

 

40,000 Min. 45,000 – 70,000 Typical

100,000 Typical

Above 1

 

80,000 – 90,000 Typical

Tensile Strength: The maximum load in tension (pulling apart) which a material can withstand before breaking or fracturing.
Yield Strength: The maximum load at which a material exhibits a specific permanent deformation
Proof Load: An axial tensile load which the product must withstand without evidence of any permanent set.

 

 


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