When you need Torx Countersunk Head Screw — GB/T 2673 / ISO 14583 (Series 023) in the M20 size, the controlling values come from GB/T 2673 / ISO 14583. This page lists them in one place — pitch, head geometry, tool size and the matching hole.
M20 Dimensional Row (GB/T 2673 / ISO 14583)
| 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 Torx Countersunk Head Screw — GB/T 2673 / ISO 14583 (Series 023)
The hex socket for M20 Torx Countersunk Head Screw — GB/T 2673 / ISO 14583 (Series 023) 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 Torx Countersunk Head Screw — GB/T 2673 / ISO 14583 (Series 023)
M20 Torx Countersunk Head Screw — GB/T 2673 / ISO 14583 (Series 023) are commonly specified for heavy assembly and large machine mounts.
Installation Tips for M20 Torx Countersunk Head Screw — GB/T 2673 / ISO 14583 (Series 023)
- 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.
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.