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Bolt Grade Markings and Properties

 
 
A quick rule-of-thumb:
The number of hash marks on the head +2 is the grade of bolt.
 
Head Markings
Grade or Class
Material
Nominal Size Range
(Inches)
Mechanical Properties
Proof Load (psi)
Minimum Yield Strength (psi)
Minimum Tensile Strength (psi)
American
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
 
80,000 – 90,000
100,000 – 125,000
3/4 thru 1
 
45,000 – 70,000
100,000
Above 1
 
80,000 – 90,000
Metric

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
 
80,000 – 90,000
100,000 – 125,000
3/4 thru 1
 
45,000 – 70,000
100,000
Above 1
 
80,000 – 90,000
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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Page last updated 10/27/2007