bolts: metric standards

Standards for metric bolts are set by the ISO. In metric bolts, a grade is called a “property class.” A property class designation consists of two numbers separated by a decimal point.

• The number before the decimal point is one-hundredth of the nominal tensile strength of the bolt in newtons per square millimeter.
• The number after the decimal point is the ratio between the nominal yield stress and the nominal tensile strength, times ten.

Bolts in property classes 4.6, 5.6, and 8.8 and above must have the property class marked on the head of the bolt. Property class 6.8 roughly corresponds to SAE grade 2; 8.8 to SAE 5; and 10.9 to SAE 8.

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Last revised: 18 November 2003.