I'll be sure to remember that the next time I see a steel bolt cleanly pull the threads out of aluminum.

Lets see, given your formula, a typical 5mm muffler bolt would have just over 4 threads holding into the aluminum cylinder. Is that really enough? I have rarely seen any engine or muffler supplied with bolts that had that little thread engagement and when I did thought it was an error on the vendor's part.

I'll leave it at that.