Our Apple Watch Bands fit ALL Apple Watch Series.
38mm / 40mm / 41mm Fits Apple Watch Bands in size 38mm, 40mm and 41mm 
42mm / 44mm / 45mm Fits Apple Watch Bands in size 42mm, 44mm and 45mm

 

As each Apple Watch series changes the Bezel Size (Size of Gaps between screen and edge of the watch), each screen is 'larger'. This does not however alter the physical shell size of the Apple Watch, meaning that all Bands are interchangeable across all series.