Many steel bolts carry a property class on the head. It states how much the bolt holds and must not be undercut in a replacement.
How to read the property class
To ISO 898-1, the first number times 100 gives the nominal tensile strength in megapascals, the product of both numbers times 10 the nominal yield or proof strength. A bolt 8.8 thus has a nominal 800 megapascals tensile strength and 640 megapascals proof strength, a 10.9 has 1000 and 900; the minimum values in the standard are slightly higher. The nut should have at least the matching class, for example 8 for 8.8 and 10 for 10.9.
High-strength bolts from 10.9 are prone to hydrogen embrittlement when electroplated with zinc; zinc flake coatings are often used instead. Stainless bolts are designated differently to ISO 3506, for example A2-70 or A4-80.
What a request for bolts should contain
- standard or type, thread and length
- property class or stainless grade
- coating, for example zinc-plated or zinc flake
- matching nuts and washers
- quantity per size
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