On the bench specifying M20 Phillips Countersunk Machine Screw — GB/T 819.1 / ISO 7046 (Series 029)? This page gives the controlling dimensions for the M20 size of Phillips Countersunk Machine Screw — GB/T 819.1 / ISO 7046 (Series 029) (to GB/T 819.1 / ISO 7046).
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 029)
The hex socket for M20 Phillips Countersunk Machine Screw — GB/T 819.1 / ISO 7046 (Series 029) 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 029)
M20 Phillips Countersunk Machine Screw — GB/T 819.1 / ISO 7046 (Series 029) are commonly specified for heavy assembly and large machine mounts.
Mating Parts for M20
For M20, pair with a M20 hex nut (ISO 4032 / DIN 934) and, where used, a M20 flat washer (ISO 7089 / DIN 125A) under the head and under the nut.
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.