The 41 mm bands work with 38 mm and 40 mm cases; the 45 mm bands work with 42 mm and 44 mm cases. Any 38 mm or 42 mm Apple Watch strap will fit an Apple Watch of the same size. If you have a single loop or a single braided bow, simply pull the lower part of the band to stretch it over your wrist when you put it on and take it off. There's no difference between the Apple Watch Series 4, Series 5 or Series 6 because they're all available in 40mm and 44mm cases.
If you're the same size as the new Apple Watch, your existing straps should fit seamlessly. Another possible cause of discomfort is having your Apple Watch too tight or too loose. A band that is too tight can cause skin irritation. A band that is too loose can cause chafing.
If you feel redness, swelling, itching, or any other irritation, see your doctor before putting your Apple Watch back on. Like the Series 7 and Watch SE models, you can purchase an additional sports strap, a single loop, or a different strap separately. The Apple Watch case, the nylon fabric, the Milanese bow, the modern buckle and the leather strap contain traces of acrylates and methacrylates from the adhesives. If you have an older Apple Watch Series 0, 1, 2 or 3, the straps should be 38 mm or 42 mm for the case.
For best results, the back of the Apple Watch needs to come into contact with the skin for functions such as Wrist Detect, the Taptic Engine, and electrical and optical heart sensors. The Nike Watch SE models have the same hardware as the Apple Watch SE, so they don't have an always-on screen, blood oxygen monitoring or ECG, but they do have functions such as fall detection, always-on altimeter and integrated compass. The sports strap is an adjustable strap made of fluoroelastomer and comes in two sizes to fit smaller and larger Apple Watch models. You can try on an Apple Watch band if you have an Apple store nearby, but if you don't have one, you have to measure a little larger so Apple doesn't ship the wrong size.
If you have an Apple Watch series 1, 2 or 3, choose the size of 41 mm for the 38 mm model and the size of 45 mm for the 42 mm models. Two colors are available for both the 38 mm and 42 mm watches, although it also works with the Series 7 and Watch SE models. This is because when Apple slightly increased the size of the Apple Watch case, it kept the same strap size. The non-sports straps come in different sizes (and it is also possible to purchase additional links for the 42 mm stainless steel link bracelet).
The Apple Watch Nike is one of the special edition ranges of the Apple Watch, created in partnership with Nike, as you've probably guessed from its name. The Apple Watch SE is between Series 7 and Series 3, and offers the same design as the previous Series 6 with a larger screen, along with several of its functions, but not as stylized as the Series 7 in terms of screen. The always-on screen of Series 7 is lost, as well as the blood oxygen monitoring and the electrical heart rate sensor for performing an ECG, and there aren't as many finishing options as Series 7 (models 14 instead of 23), but otherwise, the Watch SE is a smartwatch full of features. As for the Apple Watch Series 4, it has been updated to a new size (40 mm and 44 mm instead of 38 mm and 42 mm) and the old straps fit the new ones.
Not all Apple Watch straps are available in all sizes and not all straps are compatible with both models.
