For Square Nuts, DIN 557 defines dimensions, tolerances and product grades. The sections below describe its scope, what it does NOT cover, and the equivalents across DIN, ISO and ASME.
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 |
Equivalent Standards
Where direct equivalents exist (ISO ↔ DIN, ISO ↔ ASME), they are listed on the parent Square Nuts page. Always confirm against the dimensions on this page, since some "equivalent" standards differ in tolerances and head geometry.
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.