This is different from the Series 7, Series 8 ... Watch Ultra and Ultra 2 each feature a 49mm case. However, straps that fit 44mm/45mm/46mm Apple Watch models will also work with the Ultra ...
Older versions, like the Apple Watch Series 3, came in 42mm and 38mm case options ... while the Series 7, 8, and 9 are available in 41mm and 45mm sizes. So while it’s technically possible ...
It's important to consider compatibility and case sizing before buying. The Apple Watch Series 9 comes in 45mm or 41mm display options, while the second-gen SE is available in 44mm or 40mm.