Is there any different between Apple Watch Series 1, 2, 3, 4 and 5?

Actually, All Apple Watch Series are offer only two different size. They are,

- Apple Watch Series 1, 2, 3 - (Apple Watch 38mm & Apple Watch 42mm)

- Apple Watch Series 4 & 5  - (Apple Watch 40mm & Apple Watch 44mm)

The different between Series 1, 2, 3, 4 and 5 is the watch size. However, all series of Apple Watch are sharing the same size adapters.

Which means,

   - Apple Watch 38mm Watch strap are inter-changeable with Apple Watch 40mm. 

   - Apple Watch 42mm Watch Band are inter-changeable with Apple Watch 44mm.

Apple just enlarge the surface of the watch dial but didn't change the adapter at all. It help to make sure all watch straps are compatible on all version of Apple Watch.

******** Update about the different between Rose Gold - Apple Watch Series 1, 2 and 3, 4 and 5. *********

Apple does make the different color tone for the Rose gold version between series 1, 2 and 3, 4 and 5. Be sure to pick the correct series when you purchase the watch strap. It will have a big different on rose gold adapter on your Apple Watch Band.