Inch vs. Metric Strength Grades for Fasteners

DID YOU KNOW?

Inch Fasteners vs. Metric Fasteners

Q: I’m specifying the strength of a metric fastener and need your help. Is Class 8.8 the same as Grade 8?

A: The answer is no. Class 8.8 is not the same as Grade 8.

Confused…?

They sound so similar I know, but they are quite different. When specifying fasteners and their strengths it helps to remember that “Grades” specifically refers to Fasteners in Inch sizes and is referencing the ASTM, (the American Society for Testing and Materials), standard.

Whereas “Classes” when referencing the strength of steel fasteners is technically referencing the strength standard for metric fasteners, specifically a DIN or ISO Standard. DIN stands for “Deutsches Institut für Normung” which translates to the “German Institute for Standardization.” ISO stands for “International Organization for Standardization.”

Synopsis

The similarity in names is purely coincidental and the Metric Class 8.8 is not as strong as the Inch Grade 8. As you can see from the table below, a metric Class 8.8 is the equivalent of a Grade 5, not a Grade 8.

Please see the table below for guidance.