Hobson tightening torque chart
Stainless Socket Head Cap Screw Tightening Torque Chart, Class 50, 70 and 80
A one-page Hobson technical chart of recommended tightening torque for stainless steel socket head bolts. For each size from M3 to M39 it lists the pitch, stress area and torque for property class 50, 70 and 80.
What this covers
- Torque by size and class
- Pitch and stress area
- Notes on lubrication
Key things to remember
The essentials from this document in plain words. Check the full document before you rely on a figure.
- Covers M3 to M39 in stainless property classes 50, 70 and 80.
- Examples, class 70: M6 7.1Nm, M8 17.1Nm, M10 33.9Nm, M12 59.2Nm, M16 147.0Nm, M20 286.7Nm.
- Class 80 at M10 is 45.2Nm and at M12 78.9Nm; class 50 at M10 is 15.8Nm and at M12 27.6Nm.
- The figures assume a k factor of 0.2: burr-free threads and a good quality molybdenum disulphide (MoS2) lubricant. Stainless that is not lubricated or coated often seizes and can show k factors over 0.35.
- The values are a guide only, based on the first tightening of single assemblies in isolation.
Who it helps: Fitters and fabricators tightening stainless socket head screws.
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This document is published by Hobson Engineering, who supply this range to us. We show it here in full so you can read it next to the product; the summary above is ours. Read it on this page or download the PDF. For the most current version, ask us.