Watch
Do you need to purchase an Hermès case in order to pair the Hermès leather bands to a standard series seven watch
You can match most bands with any Apple Watch Series 3 or newer case of the same size. The 41mm bands work with 38mm and 40mm cases; the 45mm bands work with 42mm and 44mm cases.
According to:
https://www.apple.com/shop/watch/bands/hermès
The Hermes band "Works with most versions of Apple Watch."