Bolt Strength Chart and Grade Marking Chart

What is Bolt Strength Chart?

A bolt strength chart is an important tool for calculating the tension or clamp force that a bolted joint can withstand. It is used to select the correct size and type of bolt for specific applications, ensuring that the joint will be strong enough to handle any load it may incur.

The below bolt strength chart shows the amount of tension each type of bolt can reliably take before fatiguing or breaking under stress.

Commonly used Bolt Grades

The most commonly used bolt grades are:

  1. Grade 2,
  2. Grade 5,
  3. Grade 8,
  4. Grade 307A,
  5. Grade A325,
  6. Grade 651.

US Bolts

Marking on Bolt Head Grade &
Material
Nominal Size
(in inches)
Mechanical Properties
Proof Load
(Ksi)
Minimum Yield Strength
(Ksi)
Minimum Tensile Strength
(Ksi)
307A bolt head jpg Bolt Strength Chart and Grade Marking Chart

307A

Low carbon steel
1/4″ to 4″ N.A. N.A. 60
grade 2 no marking 1 jpg Bolt Strength Chart and Grade Marking Chart
without Markings

Grade- 2

Low/ medium carbon steel
1/4″ to 3/4″ 55 57 74
Over 3/4″ to 1.5″ 33 36 60
grade 5 bolt head 1 jpg Bolt Strength Chart and Grade Marking Chart
3 visible Radial Lines

Grade 5

Medium carbon steel, quenched & tempered
1/4″ to 1″ 85 92 120
Over 1″ to 1.5″ 74 81 105
grade 8 bolt head 1 jpg Bolt Strength Chart and Grade Marking Chart
6 visible Radial Lines

Grade 8

Medium carbon alloy steel, quenched & tempered
1/4″ to 1.5″ 120 130 150
A325 bolt head jpg Bolt Strength Chart and Grade Marking Chart

Grade A325

Carbon or alloy steel with or without boron
1/2″ to 1.5″ 85 92 120
Markings on stainless steel Vary

18-8 (304) & 316 Stainless

Steel alloy with chromium and nickel
All sizes thru 1″ N/A minimum 20 but 65 Typical minimum 65 but 100 – 150 Typical
A651 bolt head jpg Bolt Strength Chart and Grade Marking Chart

651 Silicon bronze

silicon bronze bolt
1/4″ to 3/4″ N.A. 55 70
7/8″ to 1.5″ N.A. 40 55
aluminum 2024 bolt head jpg Bolt Strength Chart and Grade Marking Chart

Aluminum Grade 2024

Aluminum bolt
All sizes N.A. 36 55

Metric Bolts

Marking on bolt head Bolt grade &
Material
Nominal bolt Size
(mm)
Mechanical Properties
Proof Load
(N/mm2)
Minimum Yield Strength
(N/mm2)
Minimum Tensile Strength
(N/mm2)
8.8

8.8 Class

Q &T Medium carbon steel
Almaximum 16 mm 575

650

800

16 to 72 mm 600 650 830
10.9

10.9 Class

Q & T ( quenched & tempered)
5mm – 100mm 830

940

1040

12.9

12.9 Class

Q & T ( quenched & tempered) Alloy steel,
1.6 to 100 mm 970

1100

1220

generally marked A-4 or A-2

A-2 & A-4 Stainless

stainless steel
sizes up to 20 mm N/A

minimum 210
450 generally

minium 500
700 generally


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