Apple’s website on their product dimensional drawings. I had no idea they published this to the general public. This makes complete sense to foster their huge third party cases, skins, etc.
The detail here is amazing - have a look at the Apple Watch Ultra 3 and the level of detail. Imagine you’re the manufacturer and this is the spec you have to meet. Of course, they will have tolerances but still this is incredible. I wonder what the accepted rejection rate is?