A strength designation for metric steel fasteners. For bolts, the first number times 100 gives nominal tensile strength in megapascals and the digit after the point times ten gives the yield-to-tensile ratio as a percentage, so class 10.9 means about 1,000 MPa tensile and 900 MPa yield. Nuts carry a single number, such as 8 or 10, matched to the bolt class. Stainless metric fasteners use a different scheme, such as A2-70.
Property class on those caliper bolts is 10.9, don't swap in 8.8s from the general bin just because the thread matches.
Also heard as
- metric grade
Do not mix it up with
- SAE grade: SAE grades are the inch system, marked with radial lines on the head instead of numbers.
Related terms
SAE grade
The inch bolt strength system, chiefly Grades 2, 5 and 8, identified by radial lines on the head.
Head marking
The grade symbols and maker's mark stamped on a bolt head, the main clue to its strength once it leaves the box.
Tensile strength
The maximum pulling load a fastener can take before breaking, stated as stress over its tensile stress area.
Proof load
The tensile load a full-size fastener must hold without measurable permanent stretch, about 90 percent of yield.