I don’t know why, but I’ve saved a half-dozen of those useless nuts they include with new inner tubes. I keep them, no ironic pun intended, in a glass jar with my bike lock keys.
The other day one of the bottle cages on the Trek pulled free over a couple of years worth of hard use. I was set to pitch it, until I remembered those useless nuts. They make excellent washers, and it just so happens that they fit perfectly inside the bottle cage indents:
Bottle cage securely fastened.
A while back, the bolt that holds my derailleur cable guide to my frame felt like it was stripped after I’d taken the assembly apart for cleaning. I was relegated to the fear that I’d have to replace the boss in the frame – not a minor project in a carbon fiber frame.
I took the bike to the shop to have the owner give it a once-over. He reached for a longer bolt and one of those useless nuts used as a washer again:
…And Bob’s your uncle. Those nuts aren’t useless, I definitely recommend hanging on to a few of them. They do come in handy every now and again.