Bolt Grade Markings and Strength ChartHead MarkingsGrade or ClassMaterialNominal Size Range(Inches)Mechanical Properties

Proof Load(psi)Minimum Yield Strength(psi)Minimum Tensile Strength(psi)

American Bolts

No MarkingsGrade 2Low or Medium Carbon Steel1/4 thru 3/455,00057,00074,000

Over 3/4 thru 1-1/233,00036,00060,000

3 Radial LinesGrade 5Medium Carbon Steel, Quenched and Tempered1/4 thru 185,00092,000120,000

Over 1 thru 1-1/274,00081,000105,000

6 Radial LinesGrade 8Medium Carbon Alloy Steel, Quenched and Tempered1/4 thru 1-1/2120,000130,000150,000

Stainless markings vary. Most stainless is non-magnetic18-8 StainlessSteel alloy with 17-19% Chromium and 8-13% Nickel1/4 thru 5/840,000 Min. 80,000 90,000 Typical100,000 125,000 Typical

3/4 thru 140,000 Min. 45,000 70,000 Typical100,000 Typical

Above 180,000 90,000 Typical

Metric Bolts

8.8Class 8.8Medium Carbon Steel, Quenched and TemperedAll Sizes thru 1-1/285,00092,000120,000

10.9Class 10.9Alloy Steel, Quenched and TemperedAll Sizes thru 1-1/2120,000130,000150,000

Stainless markings vary. Most stainless is non-magneticA-2 StainlessSteel alloy with 17-19% Chromium and 8-13% Nickel1/4 thru 5/840,000 Min. 80,000 90,000 Typical100,000 125,000 Typical

3/4 thru 140,000 Min. 45,000 70,000 Typical100,000 Typical

Above 180,000 90,000 Typical

Yield Strength:The maximum load at which a material exhibits a specific permanent deformation

Tensile Strength:The maximum load in tension (pulling apart) which a material can withstand before breaking or fracturing.

Proof Load:An axial tensile load which the product must withstand without evidence of any permanent set.