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Numbers or radial lines on a head giving tensile strength.
Also known as: Property class marking, Grade 8 bolt
A bolt's head carries its strength grade — a decimal number in the metric system, radial lines in the imperial one. Substituting a lower grade in a structural joint is a failure waiting to happen, and the marking is the only way to tell two identical-looking bolts apart.
States a bolt's tensile strength class, as a decimal figure on metric bolts and as radial lines on imperial ones.
Contexts: Technical drawing
Is the only visible difference between bolts of the same size and different strengths, so the marking rather than the appearance governs where a bolt may be used.
Contexts: Technical drawing
A number with a decimal point, or three to six short radial lines, raised on the flat top of a bolt head.