On the 617.952 Manifold Studs when I pullded 2 of mine off I found that there is only about 4 good threads that screw into the Cylinder Head.

I also looked around for the Torque but never found it in anythig official. But they cannot be torqued to the torque from a generic chart based on their threads and diameter.

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84 300D, 82 Volvo 244Gl Diesel