US Bolts

Head Marking

Grade and
Material

Nominal Size Range
(inches)

Mechanical Properties

Proof Load
(psi)

Min. Yield Strength
(psi)

Min. Tensile Strength
(psi)

No Markings

Grade 2

Low or medium carbon steel

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

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

1/4 thru 1-1/2

120,000

130,000

150,000

Stainless markings vary. Most stainless is non-magnetic

18-8 Stainless

Steel alloy with 17-19% Chromium and 8-13% Nickel

All Sizes thru 1

20,000 Min. 65,000 Typical

65,000 Min. 100,000 – 150,000 Typical