ISO 3506 Stainless - A2 / A4
ISO 3506 describes stainless fasteners with a steel group and a strength class, for example A2-70: A2 is the 304-type group; 70 means 700 MPa tensile.
Common classes (ISO 3506-1)
| Class | Group | Tensile Rm (min) | Yield Rp0.2 (min) |
|---|---|---|---|
| A2-50 / A4-50 | Annealed | 500 MPa | 210 MPa |
| A2-70 / A4-70 | Cold worked | 700 MPa | 450 MPa |
| A2-80 / A4-80 | Strain hardened | 800 MPa | 600 MPa |
A2 = 304-type; A4 = 316-type (with molybdenum).
These tables carry the same figures as the printed sheet below.
The printed sheet
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Text version of this sheet
ISO 3506 · metric stainless property classes
What it is
FIELD IDENTIFICATION
ISO 3506 describes stainless fasteners with a steel group and a strength class, for example A2-70: A2
is the 304-type group; 70 means 700 MPa tensile.
MFG
MFG
A2-70
A4-80
A2-70
A4-80
Steel group + strength class, e.g. A2-70, A4-80
Common classes (ISO 3506-1)
Class
Group
Tensile Rm (min)
Yield Rp0.2 (min)
A2-50 / A4-50
Annealed
500 MPa
210 MPa
A2-70 / A4-70
Cold worked
700 MPa
450 MPa
A2-80 / A4-80
Strain hardened
800 MPa
600 MPa
A2 = 304-type; A4 = 316-type (with molybdenum).
Key points
A4-80 is the upgrade when more clamp load is needed from 316.
The 2020 edition of ISO 3506 added property class 100 and duplex (austenitic-ferritic) stainless grades.
Governing standards: ISO 3506-1:2020; ISO 3506-2:2020 (nuts). 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-3BCCAC · thefastenerapp.com/fastener-guide/technical-reference/iso-3506-stainless-a2-a4 · © The Fastener App. Reference only — verify the current governing standard, drawing and manufacturer data before specifying or installing.
