The Apple Watch straps fit different sizes of the Apple Watch. This way, you can also wear an Apple Watch 38mm strap on the Apple Watch 40mm. It works the other way around as well. Watch straps for the Apple Watch 40mm also fit the Apple Watch 38mm. So, if you have an Apple Watch 40mm and you want to buy a 38mm strap, you can. You'll have a lot of options for your Apple Watch. This way, you can always find a suitable Apple Watch strap for every occasion. The straps are made by Apple, so you can be sure that they will fit on your Apple Watch.