Specification summary of GB/T 6173 as applied to hex bolt: the dimensions the standard controls, the full specified size range, and the equivalent DIN/ISO/ASME designations.
GB/T 6173 — Scope
GB/T 6173 is "Fasteners — Hexagon thin nuts with metric fine pitch thread — Product grades A and B". GB/T 6173 is the Chinese national adoption of the same document.
Material, property class, surface finish and packaging are governed by separate documents — ISO 898-1 and ISO 898-2 for mechanical property classes, ISO 4042 for electroplated finishes.
Tolerance & Product Grades
GB/T 6173 defines product grades A and B. The grade sets how closely the finished part has to follow the nominal dimensions; it is not a strength rating.
Dimensions Specified by GB/T 6173
| Size | Pitch (mm) | Nominal diameter d (mm) | Length L (mm) | Width across flats s (mm) | Width across corners e (mm) | Head height k (mm) |
|---|---|---|---|---|---|---|
| M3 | 0.5 | 3 | 20 | 5.5 | 6.01 | 2.0 |
| M4 | 0.7 | 4 | 25 | 7.0 | 7.66 | 2.8 |
| M5 | 0.8 | 5 | 30 | 8.0 | 8.79 | 3.5 |
| M6 | 1.0 | 6 | 40 | 10.0 | 11.05 | 4.0 |
| M8 | 1.25 | 8 | 50 | 13.0 | 14.38 | 5.3 |
| M10 | 1.5 | 10 | 60 | 16.0 | 17.77 | 6.4 |
| M12 | 1.75 | 12 | 80 | 18.0 | 20.03 | 7.5 |
| M14 | 2.0 | 14 | 80 | 21.0 | 23.36 | 8.8 |
| M16 | 2.0 | 16 | 100 | 24.0 | 26.75 | 10.0 |
| M18 | 2.5 | 18 | 100 | 27.0 | 30.14 | 11.5 |
| M20 | 2.5 | 20 | 120 | 30.0 | 33.53 | 12.5 |
| M24 | 3.0 | 24 | 150 | 36.0 | 39.98 | 15.0 |
| M30 | 3.5 | 30 | 180 | 46.0 | 50.85 | 18.7 |
| M36 | 4.0 | 36 | 200 | 55.0 | 60.79 | 22.5 |
Equivalent Standards
Where direct equivalents exist (ISO ↔ DIN, ISO ↔ ASME), they are listed on the parent Hex Bolt — GB/T 6173 / ISO 8675 (Series 057) page.
Always confirm against the dimensions on this page, since some "equivalent" standards differ in tolerances and head geometry.
Companion Standards
GB/T 6173 controls only the geometry of hex bolt — gb/t 6173 / iso 8675 (series 057). The mechanical strength is set by ISO 898-1 (bolts, screws and studs) or ISO 898-2 (nuts); the surface finish is governed by separate finish standards such as ISO 4042 for electroplating. For corrosion testing, the relevant document is ISO 9227 (neutral salt spray).
Custom manufacturing · Made to drawing
Need a bolt to this standard in a non-standard size?
Parts built to GB T 6173 are already in the catalog, so a special is usually a variation on existing tooling rather than a new design — which is what keeps the cost down. Made by cold heading or hot forging.
Minimum order from 2,000 pieces; samples within 7 days of drawing approval.
