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Bolt Grade Markings and Strength Chart
SpeedMart Tech Team

Bolt Grade Markings and Strength Chart

Head Marking

Grade/Class,
Material

Nominal Size Range
(inches)

Mechanical Properties

Proof Load
(psi)

Min. Yield Strength
(psi)

Min. Tensile Strength
(psi)

US Bolts


No Markings

Grade 2

Low or medium carbon steel, not for use on race cars.

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, do to the stress and vibrations involved in racing these are not recommended for use on race cars.

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, highly recommended for use in racing.

1/4 thru 1-1/2

120,000

130,000

150,000

Hex Bolts
Hex bolts are measured from under the head to the tip of the bolt.

For fasteners that are designed to be countersunk, the measurement is made from the point on the head where the surface of the material is, to the end of the fastener

Countersunk