I'll bet Daddy is right. There are only so many sizes. I started, long ago, tossing all spare metric bolts into a jar (empty peanut butter jar) so I now have a pretty decent collection of metric bolts of various sizes and heads. And when I strip a BSO from the recycling station I save all the hardware as well as any components that look like they'd be useful. I rarely have trouble finding a replacement for a missing bolt. And shortening a bolt to the length needed is easy. Measure twice, cut once. Making one longer takes more time......

I have similar collections of metric nuts and metric washers.