GB covers the dimensional requirements for socket head shoulder screw. Reproduced below: the complete size table, the tolerance grades, and the companion and equivalent standards referenced when ordering to this document.
GB — Scope
GB specifies the dimensions and tolerances of socket head shoulder screw — gb/t 5281 / iso 7379 (series 017). 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
GB, alongside the related GB/T 5281 / ISO 7379 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 GB
| Shoulder dia (mm) | Thread size | Pitch (mm) | Shoulder length (mm) | Head dia dk (mm) | Head height k (mm) | Reference standard |
|---|---|---|---|---|---|---|
| 5 | M4 | 0.7 | 16 | 9.5 | 5.3 | ISO 7379 / GB/T 5281 |
| 6 | M5 | 0.8 | 20 | 11.0 | 6.5 | ISO 7379 / GB/T 5281 |
| 8 | M6 | 1.0 | 25 | 13.0 | 8.0 | ISO 7379 / GB/T 5281 |
| 10 | M8 | 1.25 | 30 | 16.0 | 10.0 | ISO 7379 / GB/T 5281 |
| 12 | M10 | 1.5 | 40 | 18.0 | 12.0 | ISO 7379 / GB/T 5281 |
| 16 | M12 | 1.75 | 50 | 24.0 | 16.0 | ISO 7379 / GB/T 5281 |
| 20 | M16 | 2.0 | 60 | 30.0 | 20.0 | ISO 7379 / GB/T 5281 |
| 25 | M20 | 2.5 | 80 | 36.0 | 25.0 | ISO 7379 / GB/T 5281 |
Companion Standards
GB controls only the geometry of socket head shoulder screw — gb/t 5281 / iso 7379 (series 017). 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 GB
Choose GB for international engineering work and OEM supply where ISO standards are the contractual reference. It is the default modern specification for socket head shoulder screw — gb/t 5281 / iso 7379 (series 017).