ENGINEERING TOOL
M33 Bolt Torque Chart: Specs, Values & Settings
Class 8.8 · Target preload (kN) 310.9
| Dry / Black | 2052 N·m 1847–2257 |
| Electro Zinc | 1744 N·m 1539–2052 |
| Hot-Dip Galv. | 2257 N·m 1847–2565 |
| Oiled | 1334 N·m 1231–1539 |
M33 bolt torque spec: class 8.8 dry is 2052 N·m (1513 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 ≈ 2052 N·m (1847–2257); 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 | 165.2 | 1090 981–1199 | 927 818–1090 | 1199 981–1363 | 709 654–818 | 545 436–654 |
| 8.8 | 640 | 310.9 | 2052 1847–2257 | 1744 1539–2052 | 2257 1847–2565 | 1334 1231–1539 | 1026 821–1231 |
| 10.9 | 940 | 456.7 | 3014 2713–3315 | 2562 2260–3014 | 3315 2713–3767 | 1959 1808–2260 | 1507 1206–1808 |
| 12.9 | 1100 | 534.4 | 3527 3174–3880 | 2998 2645–3527 | 3880 3174–4409 | 2292 2116–2645 | 1763 1411–2116 |
| A2-70 | 450 | 218.6 | 1443 1299–1587 | 1226 1082–1443 | 1587 1299–1804 | 938 866–1082 | 721 577–866 |
| A4-80 | 600 | 291.5 | 1924 1731–2116 | 1635 1443–1924 | 2116 1731–2405 | 1250 1154–1443 | 962 770–1154 |
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 (M33 × 2 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 M33 As = 761 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 | 181.1 | 1195 1076–1315 | 1016 897–1195 | 1315 1076–1494 | 777 717–897 | 598 478–717 |
| 8.8 | 640 | 340.9 | 2250 2025–2475 | 1913 1688–2250 | 2475 2025–2813 | 1463 1350–1688 | 1125 900–1350 |
| 10.9 | 940 | 500.7 | 3305 2974–3635 | 2809 2479–3305 | 3635 2974–4131 | 2148 1983–2479 | 1652 1322–1983 |
| 12.9 | 1100 | 586 | 3867 3481–4254 | 3287 2901–3867 | 4254 3481–4834 | 2514 2320–2901 | 1934 1547–2320 |
| A2-70 | 450 | 239.7 | 1582 1424–1740 | 1345 1187–1582 | 1740 1424–1978 | 1028 949–1187 | 791 633–949 |
| A4-80 | 600 | 319.6 | 2109 1899–2320 | 1793 1582–2109 | 2320 1899–2637 | 1371 1266–1582 | 1055 844–1266 |
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 (M33 As = 694 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. M33 Bolt Torque Chart: Specs, Values & Settings. https://www.yaxiio.com/en/tools/bolt-torque-chart/m33 (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 M33 bolt?
At 70% of Rp0.2: class 4.8 ≈ 165.2 kN, 8.8 ≈ 310.9 kN, 10.9 ≈ 456.7 kN; stainless A2-70 ≈ 218.6 kN and A4-80 ≈ 291.5 kN.
Can I use carbon-steel torque values for stainless M33 (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.
M33 Hex Bolt Weight Chart
Per-piece and per-1,000-pcs weights across the full length series of the same size.
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.