For Phillips Countersunk Machine Screw — GB/T 819.1 / ISO 7046 (Series 031), the M20 thread sits in the heavy-duty range of the catalog and is one of the most-asked phillips countersunk machine screw — gb/t 819.1 / iso 7046 (series 031) in this family. The dimensional and assembly data follow.
M20 Dimensional Row (GB/T 819.1 / ISO 7046)
| Size | Pitch (mm) | Length L (mm) | Head diameter dk (mm) | Head height k (mm) | Cross recess | Countersink angle (deg) | Reference standard |
|---|---|---|---|---|---|---|---|
| M20 | 2.5 | 120 | 36.5 | 10.0 | PH4 | 90 | ISO 7046 / GB/T 819 |
Spanner & Drive for M20 Phillips Countersunk Machine Screw — GB/T 819.1 / ISO 7046 (Series 031)
The hex socket for M20 Phillips Countersunk Machine Screw — GB/T 819.1 / ISO 7046 (Series 031) is shown in the spec table — use the matching Allen / hex key (an ISO 2936 hex key set covers the full range). A T-handle Allen key gives the best feel for setting preload by feel; for production work use a torque-controlled driver.
Hole Sizes for M20
| Coarse-thread pitch (ISO 724) | 2.5 mm |
|---|---|
| Through-hole / clearance (ISO 273 medium) | 22 mm |
| Tapping drill, coarse thread | 17.5 mm |
Tightening Torque for M20
| Class 8.8 (dry, ~µ 0.125) | ≈ 410 Nm |
|---|---|
| Class 10.9 (dry, ~µ 0.125) | ≈ 580 Nm |
| Class 12.9 (dry, ~µ 0.125) | ≈ 690 Nm |
Indicative dry-joint values. Lubrication can lower the required torque by 15–25%. Always confirm against the joint design, especially when going up a strength class.
Common Applications for M20 Phillips Countersunk Machine Screw — GB/T 819.1 / ISO 7046 (Series 031)
M20 Phillips Countersunk Machine Screw — GB/T 819.1 / ISO 7046 (Series 031) are commonly specified for heavy assembly and large machine mounts.
Installation Tips for M20 Phillips Countersunk Machine Screw — GB/T 819.1 / ISO 7046 (Series 031)
- Use a quality Allen key fully seated in the socket — partial engagement is the most common cause of stripped sockets at this size.
- For countersunk and button-head variants, chamfer the through-hole to seat the head flush without preloading the head/shank fillet.
- At M20 the stretch in the bolt becomes the controlling factor — for critical joints, use angle-controlled or stretch-controlled tightening instead of pure torque.
When to Step Up or Down from M20
When the joint preload approaches the proof load of M20 class 8.8, step up to M24 class 8.8 (or move to M20 class 10.9). When the joint is over-specified, M16 often saves weight and cost without losing the safety margin.