ASTM A325 is the international standard for heavy hex socket head cap screw — gb/t 1228 / astm a325 (series 046). This page sets out what the standard governs, the size range it specifies, and the related standards you will see referenced in datasheets.
ASTM A325 — Scope
ASTM A325 specifies the dimensions and tolerances of heavy hex socket head cap screw — gb/t 1228 / astm a325 (series 046). 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
ASTM A325, alongside the related GB/T 1228 / ASTM A325 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 ASTM A325
| Size | Pitch (mm) | Length L (mm) | Head diameter dk (mm) | Head height k (mm) | Hex socket s (mm) | Reference standard |
|---|---|---|---|---|---|---|
| M3 | 0.5 | 20 | 5.5 | 3 | 2.5 | ISO 4762 / GB/T 70.1 |
| M4 | 0.7 | 25 | 7.0 | 4 | 3.0 | ISO 4762 / GB/T 70.1 |
| M5 | 0.8 | 30 | 8.5 | 5 | 4.0 | ISO 4762 / GB/T 70.1 |
| M6 | 1.0 | 40 | 10.0 | 6 | 5.0 | ISO 4762 / GB/T 70.1 |
| M8 | 1.25 | 50 | 13.0 | 8 | 6.0 | ISO 4762 / GB/T 70.1 |
| M10 | 1.5 | 60 | 16.0 | 10 | 8.0 | ISO 4762 / GB/T 70.1 |
| M12 | 1.75 | 80 | 18.0 | 12 | 10.0 | ISO 4762 / GB/T 70.1 |
| M14 | 2.0 | 80 | 21.0 | 14 | 12.0 | ISO 4762 / GB/T 70.1 |
| M16 | 2.0 | 100 | 24.0 | 16 | 14.0 | ISO 4762 / GB/T 70.1 |
| M18 | 2.5 | 100 | 27.0 | 18 | 14.0 | ISO 4762 / GB/T 70.1 |
| M20 | 2.5 | 120 | 30.0 | 20 | 17.0 | ISO 4762 / GB/T 70.1 |
| M24 | 3.0 | 150 | 36.0 | 24 | 19.0 | ISO 4762 / GB/T 70.1 |
| M30 | 3.5 | 180 | 45.0 | 30 | 22.0 | ISO 4762 / GB/T 70.1 |
| M36 | 4.0 | 200 | 54.0 | 36 | 27.0 | ISO 4762 / GB/T 70.1 |
Companion Standards
ASTM A325 controls only the geometry of heavy hex socket head cap screw — gb/t 1228 / astm a325 (series 046). 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 ASTM A325
Choose ASTM A325 for international engineering work and OEM supply where ISO standards are the contractual reference. It is the default modern specification for heavy hex socket head cap screw — gb/t 1228 / astm a325 (series 046).