Apple Watch Band

38mm, 40mm and 41mm Apple Watches all use the same bands

42mm, 44mm and 45mm Apple Watches all use the same bands

Your old 38mm and 40mm bands will attach, but will not look good on the 44mm Apple Watch

Hi,

This article should help answer your question:

https://support.apple.com/en-us/HT204818

Best of luck!