This is a work in progress and I will eventually make a watch strap version.
This was printed in TPU (it won't work without a flexible material). The buckle was printed in PLA but can be printed in any hard material (or use one for a watch).
I used two M2 bolts to secure the buckle to the bracelet.
There are two versions because I found that the overhang was hard to print and It would be easier to cut away the hole for the buckle tongue (see picture).
It's one of my first TPU prints so I'm still learning how to print it. I printed the bracelet vertically and avoided any kind of support.
Use supports for the buckle if you print it in the STL direction (which I think is the strongest one),