I highly recommend the book "Carroll Smiths Nuts Bolts Fasteners and Plumbing Handbook". It is written in laymans language and you dont need a phd in math or mechanical engineering to appreciate it. It is also pretty entertaining. And short.

All bolts stretch to a cetain extent, that is what keeps them tight. But at a certain point, the metal wont snap back from its stretched position. High strentgh bolts are harder and more prone to breaking as they are less elastic. Over tightened fasteners are a big no no with any fastener.

Its available from Amazon Books, 15 bucks or so.

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Patrick Leber
'84 190E 2.3
'83 Porsche 944 (track car)
'84 Porsche 944 (parts car)
85.5 Porsche 944 (sled)