You can match most straps with any Apple Watch Series 3 or newer case of the same size. The 41-mm bands work with 38-mm and 40-mm cases; the 45-mm straps work with 42-mm, 44-mm and 49-mm cases.
The Solo Loop and Braided Solo Loop bands are only compatible with Apple Watch SE and Apple Watch Series 4 or newer. The 40-mm and 41-mm cases work with band sizes 1–9; the 44-mm and 45-mm cases work with band sizes 1–12.