GB/T 68 covers the dimensional requirements for slotted countersunk head screw. Reproduced below: the complete size table, and the companion and equivalent standards referenced when ordering to this document.
GB/T 68 — Scope
GB/T 68 is "Slotted countersunk flat head screws — Product grade A". GB/T 68 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 68 is written to product grade A; a different grade of the same part is a different document in the family, not a variant of this one.
Dimensions Specified by GB/T 68
| Size | Pitch (mm) | Length L (mm) | Head diameter dk (mm) | Head height k (mm) | Cross recess | Countersink angle (deg) | Reference standard |
|---|---|---|---|---|---|---|---|
| M3 | 0.5 | 20 | 5.6 | 1.65 | PH1 | 90 | ISO 7046 / GB/T 819 |
| M4 | 0.7 | 25 | 7.5 | 2.2 | PH2 | 90 | ISO 7046 / GB/T 819 |
| M5 | 0.8 | 30 | 9.2 | 2.5 | PH2 | 90 | ISO 7046 / GB/T 819 |
| M6 | 1.0 | 40 | 11.0 | 3.0 | PH3 | 90 | ISO 7046 / GB/T 819 |
| M8 | 1.25 | 50 | 14.5 | 4.0 | PH3 | 90 | ISO 7046 / GB/T 819 |
| M10 | 1.5 | 60 | 18.0 | 5.0 | PH4 | 90 | ISO 7046 / GB/T 819 |
| M12 | 1.75 | 80 | 22.0 | 6.0 | PH4 | 90 | ISO 7046 / GB/T 819 |
| M14 | 2.0 | 80 | 25.0 | 7.0 | PH4 | 90 | ISO 7046 / GB/T 819 |
| M16 | 2.0 | 100 | 29.0 | 8.0 | PH4 | 90 | ISO 7046 / GB/T 819 |
| M18 | 2.5 | 100 | 33.0 | 9.0 | PH4 | 90 | ISO 7046 / GB/T 819 |
| M20 | 2.5 | 120 | 36.5 | 10.0 | PH4 | 90 | ISO 7046 / GB/T 819 |
| M24 | 3.0 | 150 | 43.5 | 12.0 | PH4 | 90 | ISO 7046 / GB/T 819 |
Companion Standards
GB/T 68 controls only the geometry of slotted countersunk head screw — gb/t 68 / iso 2009 (series 039). 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).
When to Specify GB/T 68
Choose GB/T 68 for international engineering work and OEM supply where ISO standards are the contractual reference. It is the default modern specification for slotted countersunk head screw — gb/t 68 / iso 2009 (series 039).
Custom manufacturing · Made to drawing
Need a screw to this standard in a non-standard size?
Parts built to GB T 68 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 warm forging.
Minimum order from 2,000 pieces; samples within 7 days of drawing approval.
