Silicone Sports Strap Size Guide
Using 45mm watch bands with Apple Watch Ultra:
The Ocean Band, Alpine Loop and Trail Loop are all 49mm Bands that are specifically designed for use with the Apple Watch Ultra when engaged in rugged activities like hiking, running, climbing, kiteboarding, diving and more.
Apple Watch Ultra is also compatible with 45mm Apple Watch Bands, but the 45mm watch bands should only be worn for casual, everyday wear only.