Bolt Grade Markings and Strength Chart
Head
Grade and
Nominal
Mechanical Properties
Marking
Material
Size Range
Proof
Min. Yield
Min. Tensile
Load
Strength
Strength
(inch / mm)
(psi / MPa)
(psi / MPa)
(psi / MPa)
US Bolts
Grade 2
1/4 thru 3/4
55,000/ 380
57,000 / 395
74,000 / 510
Low or medium
__________________
____________________
______________________
___________________
carbon steel
Over 3/4 thru
33,000 /230
36,000 / 250
60,000 / 415
No Markings
1‐1/2
Grade 5
1/4 thru 3/4
85,000 / 585
92,000 / 630
120,000 / 830
_________________
____________________
______________________
___________________
Medium Carbon
Steel, Quenched
and Tempered
Over 3/4 thru
74,000 / 510
81,000 / 560
105,000 / 725
1‐1/2
3 Radial Lines
Grade 8
Medium Carbon
Alloy Steel,
1/4 thru 1‐1/2
120,000 / 830
130,000 / 895
150,000 / 1,035
Quenched and
Tempered
6 Radial Lines
Metric Bolts
Class 8.8
All Sizes below
84,000 / 580
93,000 / 640
116,000 / 800
Medium Carbon
16mm
Steel, Quenched
__________________
____________________
______________________
___________________
and Tempered
16mm ‐ 72mm
87,000 / 600
96,000 / 660
120,000 / 830
8.8
Class 10.9
Alloy Steel,
5mm ‐ 100mm
120,000 / 830
136,000 / 940
151,000 / 1040
Quenched and
Tempered
10.9
12.9
Class 12.9
1.6mm ‐
Alloy Steel,
100mm
141,000 / 970
160,000 / 1100
177,000 / 1220
Quenched and
Tempered
• 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.