Smart Watch Band fits 38/40mm, this can also fit larger sizes apple watches it just won't go all the way to the end of the watch face.

This is a stretch watch band

M/L measures 6" and can stretch to 7.5" comfortably. This will fit a 7.5" to 8" wrist

Small measures 5.5" and can stretch to 7" comfortably. This will fit a 6" to 7" wrist