The spring that allows the bracelet on my watch has broken into pieces after only 15 years of use. It's a spring that can compress to a very small volume.
My first attempt at a fix was to see if they were on ebay, but no, not really. There are some springs that may work, but they weren't definitely the correct one and were very expensive. So, attempt one at making a spring was an unwound spring bent into roughly the correct shape:
Not pretty, but it sort of worked. It wasn't quite the right length, so there was still a bit of slack.
Next attempt was a few 3d printed springs in PLA:
These are much neater and a better fit as the sizes can be tuned easily and accurately. They work well too, but only for a while. The PLA seems to creep and end up in the compressed state, i.e. sort of lose it's springiness.
I've ordered some piano wire, we'll see how that works out...