ENGINEERING TOOL
2" Bolt Torque Chart (SAE Grades)
Tightening torque ranges (min–typical–max) for 2" bolts in SAE J429 Grade 2, 5 and 8, across five friction states — UNC 4.5 TPI plus the fine-thread series. K-factor method, with the metric comparison on the same page.
Next: work out your order, or check how we supply this standard
Other inch sizes
No metric counterpart within the M6–M36 range — this size sits outside the inch↔metric comparison band.
Full PDF
Download the full PDF (M6–M36, all sizes)
Printable chart covering every size in this family — click to download the PDF directly.
UNC Torque by Grade and Friction State
UNC 4.5 TPI. Tensile stress area At = 1612 mm², per the ASME B1.1 formula. Target preload = 75% of the SAE J429 proof stress × At.
Quick answer: 2"-4.5 Grade 5 · electro zinc ≈ 5326 N·m (3928 ft·lb); other grades and friction states below.
| Grade | Proof (MPa) | 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 |
|---|---|---|---|---|---|---|---|
| Grade 2 | 228 | 275 | 2794 2515–3074 | 2375 2096–2794 | 3074 2515–3493 | 1816 1677–2096 | 1397 1118–1677 |
| Grade 5 | 510 | 616.8 | 6266 5640–6893 | 5326 4700–6266 | 6893 5640–7833 | 4073 3760–4700 | 3133 2506–3760 |
| Grade 8 | 621 | 750.1 | 7621 6859–8383 | 6478 5716–7621 | 8383 6859–9526 | 4954 4573–5716 | 3811 3048–4573 |
Cell shows the typical value; the small line below is the range (min–max).
References
- SAE J429 — Mechanical and Material Requirements for Externally Threaded Fasteners (published grade proof stresses)
- ASME B1.1 — Unified Inch Screw Threads (tensile stress area formula)
- Machinery's Handbook — SAE J429 proof stress tiers and empirical K-factor ranges
- ISO 16047:2005 — Fasteners: torque/clamp force testing (K-factor measurement method)
- Machine Design — anti-seize compound friction test (K≈0.10)
- ISO 898-1:2013 — Mechanical properties of fasteners made of carbon and alloy steel (used for the ISO comparison)
UNF Fine-Thread Torque
2" has no UNF series in ASME B1.1 (the fine-thread series stops at 1-1/2"). A UNF column here would silently reuse the UNC pitch and hand you a value that describes nothing, so it is not shown — use the UNC table above.
75% vs 90% of Proof Stress
Same grade, same friction state (electro zinc, K 0.15–0.20): the standard level targets 75% of the proof stress — reusable and re-torqueable — while the yield level targets 90%, which sits close to yield and is a one-time setting.
| Grade | 75% proof (reusable) N·m | 90% proof (near yield) N·m |
|---|---|---|
| Grade 2 | 2375 | 2850 |
| Grade 5 | 5326 | 6392 |
| Grade 8 | 6478 | 7773 |
Use the 75% level for joints that will be disassembled or re-torqued, and the 90% level only where the joint is permanent and the assembly method is controlled. These are percentages of the SAE J429 proof stress, not of the yield strength.
Inch ↔ Metric and SAE ↔ ISO
Order-of-magnitude comparison only, not equivalence — the two systems specify different diameters and thread forms, so torque values must not be carried from one column to the other.
| Inch (UNC) | Nearest metric |
|---|---|
| 1/4" | M6 |
| 5/16" | M8 |
| 3/8" | M10 |
| 7/16" | M12 |
| 1/2" | M12 |
| 9/16" | M14 |
| 5/8" | M16 |
| 3/4" | M20 |
| 7/8" | M22 |
| 1" | M24 |
| 1-1/8" | M30 |
| 1-1/4" | M33 |
| 1-1/2" | M36 |
| 2" | — |
SAE Grade ↔ ISO Property Class
| SAE J429 | Approx. ISO 898-1 |
|---|---|
| Grade 2 | 4.8 |
| Grade 5 | 8.8 |
| Grade 8 | 10.9 |
Approximate only: the proof stresses are not equal even where the strength bands line up (Grade 5 sits near ISO 8.8, but the two standards publish different proof values).
Basis of Calculation & Sources
T = K · d · F: K is the nut factor, d the nominal diameter and F the target preload = SAE J429 proof stress × tensile stress area × 75% (standard level) or 90% (yield level). The stress area follows At = π/4·(d − 0.9743/n)² (ASME B1.1), which for 2"-4.5 gives At = 1612 mm². Proof stresses are the published SAE J429 values, which step down by nominal diameter tier. K follows published empirical ranges per friction state (Machinery's Handbook); the grease/MoS₂ band (K≈0.11) nearly overlaps anti-seize and is available in the calculator instead of a separate column.
Boundary: this is a simplified K-factor estimate, not a full VDI 2230 analysis (joint resilience, embedment and assembly method are not modelled). Friction is the dominant variable — no single torque value exists for a size without its friction state. Production joints follow the design specification or the manufacturer's torque table.
FAQ
What is the tightening torque for a 2"-4.5 Grade 5 bolt?
It depends on the friction state (typical values at 75% of proof stress): dry/black ≈ 6266 N·m, electro zinc ≈ 5326 N·m, hot-dip galvanized ≈ 6893 N·m, oiled ≈ 4073 N·m, anti-seize ≈ 3133 N·m. Ranges are in the table above — no single torque value exists without its friction state.
What is the target preload for a 2" bolt?
At 75% of the SAE J429 proof stress: Grade 2 ≈ 275 kN, Grade 5 ≈ 616.8 kN, Grade 8 ≈ 750.1 kN. Proof stress steps down above each grade's diameter tier (Grade 2 above 3/4", Grade 5 above 1", Grade 8 above 1-1/2"), so preload does not scale linearly with grade on the larger sizes.
What basis are these torque values calculated on?
The K-factor method T = K·d·F, with F = 75% (or 90%) of the SAE J429 proof stress × tensile stress area, and At = π/4·(d − 0.9743/n)² per ASME B1.1. Estimated values, not assembly instructions — run a full VDI 2230 analysis for critical joints.
Related References
Disclaimer: This chart is an engineering estimation for selection and budgeting only. It does not constitute assembly instructions or acceptance criteria.