M18 is one of the standard coarse-thread sizes for hex bolt, fully threaded under GB/T 5783 / ISO 4017. The sections below reproduce the dimensional row, list the matching tools and hole sizes, and summarize where this size is normally specified.
M18 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) |
|---|---|---|---|---|---|---|
| M18 | 2.5 | 18 | 100 | 27.0 | 30.14 | 11.5 |
Spanner & Drive for M18 Hex Bolt, Fully Threaded — GB/T 5783 / ISO 4017 (Series 011)
M18 Hex Bolt, Fully Threaded — GB/T 5783 / ISO 4017 (Series 011) have a width across flats of 27.0 mm — fit a 27.0 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 M18
| Coarse-thread pitch (ISO 724) | 2.5 mm |
|---|---|
| Through-hole / clearance (ISO 273 medium) | 20 mm |
| Tapping drill, coarse thread | 15.5 mm |
Tightening Torque for M18
| Class 8.8 (dry, ~µ 0.125) | ≈ 290 Nm |
|---|---|
| Class 10.9 (dry, ~µ 0.125) | ≈ 405 Nm |
| Class 12.9 (dry, ~µ 0.125) | ≈ 485 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.
Proof Load & Strength for M18
| Tensile stress area As (ISO 898-1) | 192 mm² |
|---|---|
| Proof load, class 8.8 | 115 kN |
| Proof load, class 10.9 | 159 kN |
| Proof load, class 12.9 | 186 kN |
| Min. ultimate tensile, class 8.8 | 154 kN |
Proof load = stress area × proof stress per ISO 898-1. Design joints so the working preload stays below the proof load of the selected class.
M18 Hex Bolt, Fully Threaded — GB/T 5783 / ISO 4017 (Series 011) Weight
A steel M18 hex bolt, fully threaded at the listed 100 mm length weighs approximately 257 g each — about 257 kg per 1,000 pieces. Stainless A2/A4 weighs roughly the same (density 7.9–8.0 g/cm³). Actual weight varies slightly with head form, thread and finish; use this figure for freight estimation only.
Common Applications for M18 Hex Bolt, Fully Threaded — GB/T 5783 / ISO 4017 (Series 011)
M18 Hex Bolt, Fully Threaded — GB/T 5783 / ISO 4017 (Series 011) are commonly specified for structural steelwork, heavy machinery foundations and large flange joints.
Installation Tips for M18 Hex Bolt, Fully Threaded — GB/T 5783 / ISO 4017 (Series 011)
- 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 M18 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 M18
For M18, pair with a M18 hex nut (ISO 4032 / DIN 934) and, where used, a M18 flat washer (ISO 7089 / DIN 125A) under the head and under the nut.