Metric Bolts

Head Marking

Class and
Material

Nominal Size Range
(mm)

Mechanical Properties

Proof Load
(MPa)

Min. Yield Strength
(MPa)

Min. Tensile Strength
(MPa)

Class 8.8

Medium Carbon Steel, Quenched and Tempered

All Sizes below 16mm

580

640

800

16mm - 72mm

600

660

830

Class 10.9

Alloy Steel, Quenched and Tempered

5mm - 100mm

830

940

1040

Class 12.9

Alloy Steel, Quenched and Tempered

1.6mm - 100mm

970

1100

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