Fits Apple watch size 38mm (Series 1,2,3), 40mm (Series 4,5,6,SE), 41mm (Series 7)
Fits Apple watch size 42mm (Series 1,2,3), 44mm (Series 4,5,6,SE), 45mm (Series 7,8), 49mm (Ultra)

Made from tight weave nylon for extra durability
Strong, durable and flexible for comfortable wear
Stitched construction 
Thickness: 2.5mm     
High quality stainless steel hardware

38/40/41mm: Length: 80mm and 125mm
42/44/45/49mm: Length: 80mm and 125mm

Video tutorial on how to change the strap for Apple Watch can be found