For hex bit sockets, ISO 1174 is the governing document for the dimensions listed below. Mechanical and performance requirements for this part family are set by its own standards, not by the bolt and screw property-class documents.
ISO 1174 — Scope
ISO 1174 specifies the dimensional requirements for hex bit sockets.
Material, surface condition and any performance rating are set by separate documents specific to this part family — ISO 898-1 and ISO 898-2, which govern bolt and nut property classes, do not apply here.
Tolerance & Product Grades
Tolerances for hex bit sockets are given as limits on the individual dimensions in the table rather than as a fastener product grade.
Where a general-tolerance class is cited on the drawing instead, it applies to the dimensions not otherwise toleranced.
Dimensions Specified by ISO 1174
| Hex size | Square drive | Mating socket screw | Purpose |
|---|---|---|---|
| 3 mm | 1/4 in | M4 | torque-controlled tightening |
| 4 mm | 1/4 in | M5 | torque-controlled tightening |
| 5 mm | 3/8 in | M6 | torque-controlled tightening |
| 6 mm | 3/8 in | M8 | torque-controlled tightening |
| 8 mm | 1/2 in | M10 | torque-controlled tightening |
| 10 mm | 1/2 in | M12 | torque-controlled tightening |
| 14 mm | 1/2 in | M16 | torque-controlled tightening |
Equivalent Standards
Where direct equivalents exist (ISO ↔ DIN, ISO ↔ ASME), they are listed on the parent Hex Bit Sockets page.
Always confirm against the dimensions on this page, since some "equivalent" standards differ in tolerances and head geometry.
When to Specify ISO 1174
Choose ISO 1174 for international engineering work and OEM supply where ISO standards are the contractual reference. It is the default modern specification for hex bit sockets.
