Hobson tightening torque chart
SOKO Class 12.9 Socket Screw Torque Chart: Metric Recommended Tightening Torque
Hobson's one-page chart of recommended tightening torques for the SOKO range of metric class 12.9 socket screws. It gives torque in newton metres, plain and zinc plated, for socket head cap screws, low head, countersunk and button head screws, socket set (grub) screws and shoulder screws.
What this covers
- Socket head
- Low head
- Countersunk head
- Button head
- Socket set screw (grub)
- Shoulder screw
Applies to Socket Button Screw, Socket Head Cap Screw, Socket Countersunk Screw, Grub Screws (Socket Set Screws) and Socket Shoulder Screw.
Key things to remember
The essentials from this document in plain words. Check the full document before you rely on a figure.
- Socket head cap screws, class 12.9, are listed from M1.6 to M42.
- Socket head cap screw, plain (zinc plated): M6 16.4Nm (11.5Nm), M8 39.8Nm (27.8Nm), M10 78.8Nm (55.1Nm), M12 137.4Nm (96.2Nm), M16 341.1Nm (238.8Nm), M20 665.4Nm (465.8Nm).
- Socket set (grub) screws, high grade alloy steel, take much less: M8 18.0Nm plain or 12.6Nm zinc plated, M10 36.0Nm or 25.2Nm.
- Zinc plated screws get about 30% less torque than plain ones, because zinc plating lowers the friction.
- Conditions: a guide only, for the first tightening of a single assembly on its own, using a k factor of 0.2 for plain threads (burr-free, lightly oiled) and 0.14 for zinc plated.
- Torque is only a rough way to set bolt tension: the chart does not account for the many real-world variables that change friction.
Who it helps: Fitters and machinists tightening class 12.9 socket screws.
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