M20 Hex Bolt — GB/T 5783 / ISO 4017 (Series 010) is the m20-thread variant of Hex Bolt — GB/T 5783 / ISO 4017 (Series 010) manufactured to GB/T 5783 / ISO 4017. This page focuses on the data engineers reach for at the bench: dimensional values for the M20 size, the spanner/drive that fits, and the assembly data you need to install it.
M20 Dimensional Row (GB/T 5783 / ISO 4017)
| Size | Pitch (mm) | Nominal diameter d (mm) | Length L (mm) | Width across flats s (mm) | Width across corners e (mm) | Head height k (mm) |
|---|---|---|---|---|---|---|
| M20 | 2.5 | 20 | 120 | 30.0 | 33.53 | 12.5 |
Spanner & Drive for M20 Hex Bolt — GB/T 5783 / ISO 4017 (Series 010)
M20 Hex Bolt — GB/T 5783 / ISO 4017 (Series 010) have a width across flats of 30.0 mm — fit a 30.0 mm open-ended spanner or socket. Use a 6-point socket for tight clearances and to reduce rounding; for repeated assembly choose a torque wrench so the joint preload is repeatable.
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 Hex Bolt — GB/T 5783 / ISO 4017 (Series 010)
M20 Hex Bolt — GB/T 5783 / ISO 4017 (Series 010) are commonly specified for structural steelwork, heavy machinery foundations and large flange joints.
Installation Tips for M20 Hex Bolt — GB/T 5783 / ISO 4017 (Series 010)
- Use a 6-point socket where access allows — 12-point sockets are more prone to rounding the corners on smaller sizes.
- On flanged or serrated variants, do NOT add a separate flat washer — the flange already spreads the load and the washer can defeat the locking serrations.
- 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.