I do NOT want to start an opinion-based forum similar to motor oil brands or frequency of changing etc. I suppose mechanical engineers would be best suited at answering this question.

Does anyone know if there is a steadfast rule (or even where it's printed) on thread lubrication regarding torque specifications? I know that head bolts/engine reassembly hardware should ALWAYS be lubricated and then torqued (the factory repair manuals often state that). What about other applications. Lug nuts onto wheel studs? Random fasteners on the engine that actually HAVE a torque specification? A mechanical engineer once told me that whenever a torque specification is given (regardless of how big or small the bolt is or where it is on the car), the engineers ASSUME that you as a mechanic will lubricate the threads AND the shank (or underside of the bolthead). That torque specification takes that into consideration. Is that true?

The only thing that seems to be certain is with head bolts on an engine. I've heard you should NEVER lubricate (whether it be with anti-seize or oil) lug bolts/nuts, then I have read that you should. Mike Allen of Popular Mechanics (the automotive repair editor) wrote that it's OK to lubricate the lug nut threads on a wheel and then torque them 20% beyond the torque specification to account for the lubrication. I'm all confused.

What's the standard/generally accepted rule? Is it for ALL fasteners? What type of lubrication should be used? Why do some repair manuals actually specify lubricate and torque while two-pages later, that same manual states to torque with no mention of lubrication.

Is there a website (maybe by the SAE) that clarifies this?