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Found this Guess I Need a Stronger Bolt!!





Bolt Grade Markings and Strength Chart

Head Marking Grade and
MaterialNominal Size Range
(inches)Mechanical Properties Proof Load
(psi)Min. Yield Strength
(psi)Min. Tensile Strength
(psi)US Bolts


No MarkingsGrade 2

Low or medium carbon steel

1/4 thru 3/455,00057,00074,000Over 3/4 thru 1-1/233,00036,00060,000
3 Radial LinesGrade 5

Medium Carbon Steel, Quenched and Tempered


thru 185,00092,000120,000Over 1 thru 1-1/274,00081,000105,000
6 Radial LinesGrade 8

Medium Carbon Alloy Steel, Quenched and Tempered
1/4 thru 1-1/2120,000130,000150,000Stainless markings vary. Most stainless is non-magnetic18-8 Stainless

Steel alloy with 17-19% Chromium and 8-13% Nickel
1/4 thru 5/8 40,000 Min. 80,000 – 90,000 Typical100,000 – 125,000 Typical3/4 thru 1 40,000 Min. 45,000 – 70,000 Typical100,000 TypicalAbove 1 80,000 – 90,000 TypicalHead MarkingClass and
MaterialNominal Size Range
(mm)Mechanical Properties Proof Load
(MPa)Min. Yield Strength
(MPa)Min. Tensile Strength
(MPa)Metric bolts








8.8Class 8.8

Medium Carbon Steel, Quenched and Tempered
All Sizes below 16mm580640
800




16mm - 72mm 600660830
10.9Class 10.9

Alloy Steel, Quenched and Tempered
5mm - 100mm830940
1040

12.9Class 12.9

Alloy Steel, Quenched and Tempered
1.6mm - 100mm9701100
1220
Stainless markings vary. Most stainless is non-magnetic.
Usually stamped A-2
A-2 Stainless

Steel alloy with 17- 19% Chromium and 8-13% Nickel
All Sizes thru 20mm 210 Min.
450 Typical
500 Min.
700 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.
1MPa = 1N/mm2 = 145 pounds/inch2