Coarse (0.8mm pitch) vs fine (0.5mm pitch) — how thread pitch affects torque, clamp load, and stress area.
| Class | Coarse | Area mm² | Fine | Area mm² | Diff |
|---|---|---|---|---|---|
| 4.6 | 2.4 N·m | 14.18 | 2.7 N·m | 16.13 | +13% |
| 4.8 | 3.3 N·m | 14.18 | 3.8 N·m | 16.13 | +15% |
| 5.6 | 3.0 N·m | 14.18 | 3.4 N·m | 16.13 | +13% |
| 5.8 | 4.0 N·m | 14.18 | 4.6 N·m | 16.13 | +15% |
| 6.8 | 4.7 N·m | 14.18 | 5.3 N·m | 16.13 | +13% |
| 8.8 | 6.2 N·m | 14.18 | 7.0 N·m | 16.13 | +13% |
| 9.8 | 6.9 N·m | 14.18 | 7.9 N·m | 16.13 | +14% |
| 10.9 | 8.8 N·m | 14.18 | 10.0 N·m | 16.13 | +14% |
| 12.9 | 10.3 N·m | 14.18 | 11.7 N·m | 16.13 | +14% |
Fine thread bolts have a larger tensile stress area than coarse thread bolts of the same nominal diameter. The smaller pitch means less material is removed to cut the thread, leaving more cross-section to carry load. For M5, the fine thread stress area is about 14% larger.
This larger stress area produces a higher proof load, which in turn requires higher torque to achieve the target clamp force (75% of proof load).
Coarse thread (M5 × 0.8) — the default for general-purpose use. Faster assembly, more tolerant of minor thread damage, less likely to cross-thread. Standard for structural, automotive, and general mechanical applications. Always the assumed thread pitch unless otherwise specified.
Fine thread (M5 × 0.5) — for precision applications where vibration resistance or fine adjustment matters. Common in aerospace, automotive suspension, and instruments. The smaller pitch provides finer clamping adjustment and better resistance to loosening under vibration, but is more sensitive to thread damage and cross-threading.