ISO 898-2 Metric Nut Classes
Metric nuts have their own property classes. The rule of thumb: the nut class should equal the first number of the bolt class.
Pairing (ISO 898-2)
| Bolt class | Nut class | Nut marking |
|---|---|---|
| up to 5.8 | 5 (or higher) | 5 |
| up to 6.8 | 6 (or higher) | 6 |
| 8.8 | 8 (or higher) | 8 |
| 9.8 | 9 (or higher) | 9 |
| 10.9 | 10 (or higher) | 10 |
| 12.9 | 12 | 12 |
| Thin nuts | 04 / 05 | 04 / 05 (reduced load) |
The nut class number is the highest bolt class it is designed to carry. Nut height comes in two styles: ISO 4032 style 1 (regular) and ISO 4033 style 2 (high).
These tables carry the same figures as the printed sheet below.
The printed sheet
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Text version of this sheet
ISO 898-2 · property classes for metric nuts
What it is
FIELD IDENTIFICATION
Metric nuts have their own property classes. The rule of thumb: the nut class should equal the first
number of the bolt class.
8
Nut class number on the face (class 8 shown)
Pairing (ISO 898-2)
Bolt class
Nut class
Nut marking
up to 5.8
5 (or higher)
5
up to 6.8
6 (or higher)
6
8.8
8 (or higher)
8
9.8
9 (or higher)
9
10.9
10 (or higher)
10
12.9
12
12
04 / 05
04 / 05 (reduced load)
Thin nuts
The nut class number is the highest bolt class it is designed to carry. Nut height comes in two styles: ISO 4032 style 1 (regular) and ISO 4033 style 2 (high).
Key points
A weaker nut on a strong bolt strips the nut first. Using class 6 on 10.9 is a common failure.
Thin (jam) nuts carry reduced loads regardless of material.
Governing standards: ISO 898-2:2022; ISO 898-1:2013. Editions shown are the latest confirmed as of September 2026. The drawing and the governing standard always take
precedence over this sheet.
torquing any fastener. Verify the current governing standard, project documents, OEM requirements, size, thread, coating and lot certification. To the fullest extent permitted by law, The Fastener App disclaims liability
arising from reliance on this reference.
Fastener Guide reference FG-9EE3B4 · thefastenerapp.com/fastener-guide/technical-reference/iso-898-2-metric-nut-classes · © The Fastener App. Reference only — verify the current governing standard, drawing and manufacturer data before specifying or installing.
