The criticality of nuts and bolts!

classic car fastenersclassic car fasteners

Few parts are as important in the assembly of vehicles, cars and motor bikes, as the nuts and bolts which hold them together and, at first sight, it seems that all bolts are basically the same, yet I’ve learnt that is far from the truth.

There are no fewer than 5 different threads for different uses and 10 different standard strength grades defined for each size of bolt. There are nineteen standard sizes – known as the ‘preferred ‘ sizes and ten less commonly used (the so- called ‘non-preferred’) sizes.

The situation is almost as complex with nuts, which come in a wide variety of types (full, thin, nyloc, castellated etc etc…) and 5 strength grades as well as the same range of sizes.

The difference in strength between different grades is quite dramatic with highest standard grade being capable of carrying more than three times as much load as the lowest grade.

But how do you find out what is low grade and high grade? We recently had a request to quote for a number of sizes from a motorcycle restorer. When the quote was sent I spoke with the restorer who berated me over the prices. Somewhat taken aback, I asked where he was purchasing his fasteners currently. It transpired that all his fasteners were being sourced from autojumbles and old stock, without him being aware of the grade of fastener or the manufacturing quality. I suggested to him that he might want to check his liability insurance – yet in sourcing parts for the motorbikes, he was purchasing only highest quality remanufactured items.

It does seem as though fasteners are often the last thing anyone thinks about, or indeed the one thing that is purchased on price rather than quality. Yet if the fasteners “let go” the result can be dramatic.

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