This will fit all 42mm Apple Watch models:
Original, Series 1, Series 2 & Series 3
This will fit all 44mm Apple Watch models:
Series 4 44mm
Series 5 44mm
Series 6 44mm
Apple Watch SE 44mm (1st & 2nd Gen)
This will fit all 45mm Apple Watch Models:
Series 7 45mm
Series 8 45mm
Series 9 45mm
This will also fit the:
Apple Watch Ultra (49mm)
Apple Watch Ultra 2 (49mm)
Please see screenshot for 44mm, 45mm & 49mm compatibility