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Bolt Grade Markings and Strength Chart

This technical information has been supplied by boltdepot.com

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.