TorqueSpec
Bolt torque database

Coarse vs Fine Thread Torque

Thread pitch affects stress area, which affects torque. Compare coarse and fine thread torque specifications for every metric bolt size.

M3 — 0.5mm vs 0.35mmM4 — 0.7mm vs 0.5mmM5 — 0.8mm vs 0.5mmM6 — 1.0mm vs 0.75mmM7 — 1.0mm vs 0.75mmM8 — 1.25mm vs 1.0mmM10 — 1.5mm vs 1.25mmM12 — 1.75mm vs 1.25mmM14 — 2.0mm vs 1.5mmM16 — 2.0mm vs 1.5mmM18 — 2.5mm vs 1.5mmM20 — 2.5mm vs 1.5mmM22 — 2.5mm vs 1.5mmM24 — 3.0mm vs 2.0mmM27 — 3.0mm vs 2.0mmM30 — 3.5mm vs 2.0mmM33 — 3.5mm vs 2.0mmM36 — 4.0mm vs 3.0mmM39 — 4.0mm vs 3.0mmM42 — 4.5mm vs 3.0mmM45 — 4.5mm vs 3.0mmM48 — 5.0mm vs 3.0mmM52 — 5.0mm vs 4.0mmM56 — 5.5mm vs 4.0mmM64 — 6.0mm vs 4.0mm

Coarse or fine thread?

Every ISO metric size has a standard coarse pitch (ISO 261) and one or more fine pitches (ISO 262). Fine threads have a larger tensile stress area because less material is cut away, so the same property class can carry more clamp load and the torque specification rises with it — by about 5% at M10, and by more at small sizes such as M3, where the fine pitch removes proportionally less material.

Fine threads also have a smaller helix angle, which gives finer adjustment and slightly better resistance to loosening under vibration. The trade-offs are that they strip more easily in soft materials, are harder to start without cross-threading and are less tolerant of damaged or dirty threads. Coarse thread remains the default for general engineering; fine threads are common in automotive driveline and hydraulic fittings and wherever a thin-walled part limits thread depth.

Never apply a coarse-thread torque to a fine-thread bolt or the other way round. Check the pitch with a gauge — M10×1.5 and M10×1.25 look almost identical — and use the table for that pitch.