DIN 7991 covers the dimensional requirements for countersunk socket screws. Reproduced below: the complete size table, the tolerance grades, and the companion and equivalent standards referenced when ordering to this document.
DIN 7991 — Scope
DIN 7991 specifies the dimensions and tolerances of countersunk socket screws. 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 7991, alongside the related ISO 10642 / DIN 7991 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 7991
| Size | Pitch (mm) | Head diameter dk (mm) | Head height k (mm) | Hex key s (mm) | Countersink angle (deg) | Reference standard |
|---|---|---|---|---|---|---|
| M3 | 0.5 | 6.72 | 1.86 | 2.0 | 90 | ISO 10642 / DIN 7991 |
| M4 | 0.7 | 8.96 | 2.48 | 2.5 | 90 | ISO 10642 / DIN 7991 |
| M5 | 0.8 | 11.2 | 3.1 | 3.0 | 90 | ISO 10642 / DIN 7991 |
| M6 | 1.0 | 13.44 | 3.72 | 4.0 | 90 | ISO 10642 / DIN 7991 |
| M8 | 1.25 | 17.92 | 4.96 | 5.0 | 90 | ISO 10642 / DIN 7991 |
| M10 | 1.5 | 22.4 | 6.2 | 6.0 | 90 | ISO 10642 / DIN 7991 |
| M12 | 1.75 | 26.88 | 7.44 | 8.0 | 90 | ISO 10642 / DIN 7991 |
| M14 | 2.0 | 30.0 | 8.4 | 10.0 | 90 | ISO 10642 / DIN 7991 |
| M16 | 2.0 | 33.6 | 9.3 | 10.0 | 90 | ISO 10642 / DIN 7991 |
| M20 | 2.5 | 40.32 | 11.2 | 12.0 | 90 | ISO 10642 / DIN 7991 |
| M24 | 3.0 | 47.04 | 13.0 | 14.0 | 90 | ISO 10642 / DIN 7991 |
Companion Standards
DIN 7991 controls only the geometry of countersunk socket screws. 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 7991
DIN 7991 is still widely used in European mechanical engineering and as a cross-reference on legacy drawings; its ISO equivalent is preferred for new designs.
