Could it be a lid and the hole is for steam to escape?

Awesome, thank you so much!

Oh wow, I much fuller reply than I expected. Thank you! I did read up on some stuff already and saw the nh35 suggested so I started looking for parts with that listed in the title. There’s no gotchas if I stick with those? Or do i need to make sure the parts fit together?

Like awesome! I’m considering building a custom watch. Any advice for someone with no experience?