DIN 557 is the governing dimensional standard for square nuts. This page sets out the scope of the standard, reproduces the full size table it specifies, and lists the DIN/ISO/ASME cross-references commonly cited in datasheets and drawings.
DIN 557 — Scope
DIN 557 specifies the dimensions and tolerances of square nuts. Material, property class, surface finish and packaging are governed by separate documents in the same standards family (for example ISO 898-1 for the mechanical property classes of bolts and screws).
Tolerance & Product Grades
DIN 557, alongside the related DIN 557 entries on this site, specifies product grades (typically A or B for fine work and C for general engineering) and tolerance classes for the controlling dimensions. Choose the grade against the precision your application requires.
Dimensions Specified by DIN 557
| Size | Pitch (mm) | Width across flats s (mm) | Width across corners e min (mm) | Nut height m (mm) | Reference standard | Notes |
|---|---|---|---|---|---|---|
| M5 | 0.8 | 8.0 | 11.1 | 4.0 | DIN 557 / DIN 562 | Square nut, general / channel use |
| M6 | 1.0 | 10.0 | 13.9 | 5.0 | DIN 557 / DIN 562 | Square nut, general / channel use |
| M8 | 1.25 | 13.0 | 18.0 | 6.5 | DIN 557 / DIN 562 | Square nut, general / channel use |
| M10 | 1.5 | 17.0 | 23.6 | 8.0 | DIN 557 / DIN 562 | Square nut, general / channel use |
| M12 | 1.75 | 19.0 | 26.5 | 10.0 | DIN 557 / DIN 562 | Square nut, general / channel use |
| M16 | 2.0 | 24.0 | 33.5 | 13.0 | DIN 557 / DIN 562 | Square nut, general / channel use |
| M20 | 2.5 | 30.0 | 42.0 | 16.0 | DIN 557 / DIN 562 | Square nut, general / channel use |
Companion Standards
DIN 557 controls only the geometry of square nuts. The mechanical strength is set by ISO 898-1 (bolts and screws) or ISO 898-2 (nuts); the surface finish is governed by separate finish standards (e.g. ISO 4042 for electroplating). For corrosion testing, the relevant document is ISO 9227 (neutral salt spray).
When to Specify DIN 557
DIN 557 is still widely used in European mechanical engineering and as a cross-reference on legacy drawings; its ISO equivalent is preferred for new designs.