This will work with all 40mm Apple Watch models:
Series 4 40mm
Series 5 40mm
Series 6 40mm
Apple Watch SE 40mm (1st & 2nd Gen)
This will also fit 41mm Apple Watch Models:
Series 7 41mm
Series 8 41mm
Series 9 41mm
These will also fit all 38mm Apple Watch models:
Original, Series 1, Series 2 & Series 3
Please see screenshot for 41mm & 38mm compatibility