ENGINEERING TOOL
M18 Bolt Torque Chart: Specs, Values & Settings
Class 8.8 · Target preload (kN) 86
| Dry / Black | 310 N·m 279–341 |
| Electro Zinc | 263 N·m 232–310 |
| Hot-Dip Galv. | 341 N·m 279–387 |
| Oiled | 201 N·m 186–232 |
M18 bolt torque spec: class 8.8 dry is 310 N·m (229 ft·lb). Values cover six property classes across five friction states — dry, zinc, HDG, oiled and anti-seize. K-factor method, basis fully disclosed.
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Torque by Property Class and Friction State
Quick answer: class 8.8 · dry / black ≈ 310 N·m (279–341); other classes and friction states below.
| Class | Rp0.2 (MPa) | Target preload (kN) | Dry / Black K 0.18–0.22 · N·m | Electro Zinc K 0.15–0.2 · N·m | Hot-Dip Galv. K 0.18–0.25 · N·m | Oiled K 0.12–0.15 · N·m | Wax / PTFE / Anti-seize K 0.08–0.12 · N·m |
|---|---|---|---|---|---|---|---|
| 4.8 | 340 | 45.7 | 165 148–181 | 140 123–165 | 181 148–206 | 107 99–123 | 82 66–99 |
| 8.8 | 640 | 86 | 310 279–341 | 263 232–310 | 341 279–387 | 201 186–232 | 155 124–186 |
| 10.9 | 940 | 126.3 | 455 409–500 | 387 341–455 | 500 409–569 | 296 273–341 | 227 182–273 |
| 12.9 | 1100 | 147.8 | 532 479–585 | 452 399–532 | 585 479–665 | 346 319–399 | 266 213–319 |
| A2-70 | 450 | 60.5 | 218 196–240 | 185 163–218 | 240 196–272 | 142 131–163 | 109 87–131 |
| A4-80 | 600 | 80.6 | 290 261–319 | 247 218–290 | 319 261–363 | 189 174–218 | 145 116–174 |
Cell shows the typical value; the small line below is the range (min–max).
References
- ISO 898-1:2013 — Mechanical properties of fasteners made of carbon and alloy steel
- ISO 3506-1:2020 — Mechanical properties of corrosion-resistant stainless steel fasteners (A2/A4)
- GB/T 3098.1-2010 — Mechanical properties of bolts, screws and studs (CN national standard, official full text)
- GB/T 3098.6-2014 — Mechanical properties of stainless steel bolts, screws and studs (CN, official full text)
- ISO 16047:2005 — Fasteners: torque/clamp force testing (K-factor measurement method)
- Machinery's Handbook (30th ed.) — empirical K-factor ranges
- Machine Design — anti-seize compound friction test (K≈0.10)
Fine-Thread Torque Matrix
Fine-thread series (M18 × 1.5 mm) target preload and tightening torque ranges, same basis as the coarse chart; the fine-thread stress area As follows ISO 898-1:2013 Table 6 (this page takes M18 As = 216 mm²).
| Class | Rp0.2 (MPa) | Target preload (kN) | Dry / Black K 0.18–0.22 · N·m | Electro Zinc K 0.15–0.2 · N·m | Hot-Dip Galv. K 0.18–0.25 · N·m | Oiled K 0.12–0.15 · N·m | Wax / PTFE / Anti-seize K 0.08–0.12 · N·m |
|---|---|---|---|---|---|---|---|
| 4.8 | 340 | 51.4 | 185 167–204 | 157 139–185 | 204 167–231 | 120 111–139 | 93 74–111 |
| 8.8 | 640 | 96.8 | 348 314–383 | 296 261–348 | 383 314–435 | 226 209–261 | 174 139–209 |
| 10.9 | 940 | 142.1 | 512 460–563 | 435 384–512 | 563 460–640 | 333 307–384 | 256 205–307 |
| 12.9 | 1100 | 166.3 | 599 539–659 | 509 449–599 | 659 539–748 | 389 359–449 | 299 240–359 |
| A2-70 | 450 | 68 | 245 220–269 | 208 184–245 | 269 220–306 | 159 147–184 | 122 98–147 |
| A4-80 | 600 | 90.7 | 327 294–359 | 278 245–327 | 359 294–408 | 212 196–245 | 163 131–196 |
Cell shows the typical value; the small line below is the range (min–max).
Basis of Calculation & Sources
Calculation basis
- Torque follows the K-factor (nut factor) method T = K·D·F: D is the nominal diameter and F the target preload = 70% of Rp0.2 × thread stress area (M18 As = 192 mm²).
- Yield strengths are published values from ISO 898-1 (carbon/alloy steel) and ISO 3506-1 (stainless A2/A4).
- K follows published empirical ranges per friction condition (Machinery's Handbook; the wax/PTFE/anti-seize band K≈0.10 follows Machine Design test data).
- The grease/MoS₂ band (K≈0.11) nearly overlaps anti-seize and is available in the calculator instead of a separate column.
Stainless note: A2/A4 austenitic thread pairs gall easily under frictional heating. Always apply anti-seize and follow the Wax/PTFE/Anti-seize column (K≈0.10).
Scope & limits
- This chart is a simplified K-factor estimate, not a full VDI 2230 analysis (which accounts for joint resilience, embedment and assembly method).
- Friction is the dominant variable — no single torque value exists without its friction state.
- Always follow the design specification or manufacturer torque table.
Cite this chart
YAXIIO. M18 Bolt Torque Chart: Specs, Values & Settings. https://www.yaxiio.com/en/tools/bolt-torque-chart/m18 (accessed 2026-10-29).
Free to cite and embed — attribution required: “YAXIIO” + a link to this page.
FAQ
What is the target preload for an M18 bolt?
At 70% of Rp0.2: class 4.8 ≈ 45.7 kN, 8.8 ≈ 86 kN, 10.9 ≈ 126.3 kN; stainless A2-70 ≈ 60.5 kN and A4-80 ≈ 80.6 kN.
Can I use carbon-steel torque values for stainless M18 (A2-70/A4-80)?
No. The classes have different yield strengths (A2-70 = 450 MPa, A4-80 = 600 MPa), so target preloads differ; and stainless thread pairs gall easily — always apply anti-seize and follow the Wax/PTFE/Anti-seize column (K≈0.10).
Next: work out your order, or pick the size by standard
Related References
Bolt Torque Calculator
Interactive version: fine threads, imperial, stud bolts, custom K and torque check — this size is pre-filled.
M18 Hex Bolt Weight Chart
Per-piece and per-1,000-pcs weights across the full length series of the same size.
M18 Hex Key Size Chart
Which hex key (Allen wrench) fits a socket head cap screw of the same size: socket width across flats, key long and short arm lengths, and unit weight on the GB/T 70.1 + GB/T 5356 basis.
Tap Drill for the Thread Being Tightened
The hole under the bolt: rule tap drill value plus the nearest drill bit in the set, stated ahead of the torque tables.
Disclaimer: This chart is an engineering estimation for selection and budgeting only. It does not constitute assembly instructions or acceptance criteria.