I find that especially with smaller hex cap screws the hex drive is worn out or deformed long before I reach the maximum torque that the screw could theoretically handle.
For example: I've used M5 ISO 10642 (8.8 alloy steel) screws recently which can be fastened with about 6Nm (which - if I understood it correctly - is 90% of the screw's yield strength). I found that the hex drive was starting to get deformed at around 4 - 4.5Nm and I didn't dare to fasten it any tighter fearing I'd wear out the drive (which has happened in the past with M3 and M4 screws unfortunately).

Now I could use a different grade of steel, use a different type of head (the ISO 4762 for example have a larger drive for the same thread diameter) etc., but I was wondering if there's a table for hex drives that lists the maximum torque for each drive size similar to Torx?


  • These screws are purely for mechanical fastening purposes, correct? – ThreePhaseEel Mar 3 '19 at 1:50
  • There are many available online, e.g. federalscrewproducts.com/torque-chart.htm – DrMoishe Pippik Mar 3 '19 at 3:17
  • @DrMoishePippik the table you've linked only lists torque depending on bolt size. My question is about torque depending on hex drive size (which I suspect is less that what the bolt can take, at least for common grades of steel like 8.8 or 10.9). – Clayton Louden Mar 3 '19 at 18:25
  • @ThreePhaseEel Yes, purely for mechanical fastening purposes (I wouldn't know what to use screws for otherwise) – Clayton Louden Mar 3 '19 at 18:26
  • 1
    @ClaytonLouden screws used for electrical connections have different torque requirements – ThreePhaseEel Mar 3 '19 at 18:29

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