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High Tensile Steel Question

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27/12/2022 17:42:19

Now I've done some more sums, easier than I thought. According to this, grade 8,8 M12 bolts have a proof stress of 600 MPa, recommended torque 65 lb.ft (88 Nm). EN1a has proof 230 MPa, so recommended torque would be 88*230/600=33.7 Nm. Applying this to a 3/8 square drive gives a shear stress of 187 MPa, which is too high for EN1a by a long way. There's no need to tighten them this tight obviously, 15 Nm would be OK

I'd still use M12 capheads, drill and tap say M5 concentric with the hex (not necessarily concentric with the shank, been there), make an adaptor with M5 spike, the 10 diameter to fit the hex socket, then 10 square (or 3/8 if you're really picky). Then you can tighten the capheads with a proper key, and screw in the dummies with a dab of low strength loctite. If you really want solid and a higher torque, use EN16 and adjust tightening torque appropriately. Limiting feature is still the square, 33 Nm is OK

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