If you have the smaller variant of the Apple Watch, a 38mm, 40mm, 41mm, or 42mm band from that size lineup will fit any watch. Likewise, any larger band for the 44mm, 45mm, 46mm, and 49mm range ...

The only problem with the Apple Watch’s unprecedented ubiquity is ... For the Series 4-6, case sizes were 40mm and 44mm, while the Series 0-3 were 38mm and 42mm. It can sound confusing ...

Aside from the 38mm and 42mm sizes, there were initially many models of Apple Watch Series 3 and various bands. Today, Apple only sells the 2017 model in black and white variants with Sport Bands.

The Apple Watch Series 3 is available in the UK in two sizes of 38mm or 42mm ... just be sure that you’re choosing the right strap to fit your case size (it’ll be displayed in millimetres).