Aviation grade aluminum and German Bayer TPU 2-in-1 design provides the best level of protection and scratch-resistant compatible with all kinds of watch brands. 1. German Bayer TPU material provides the best protection and durability. 2. Premium 2-in-1 aviation grade aluminum alloy + TPU design. 3. Responsive buttons. 4. Compatible with Apple Watch strap lock design. Easy to install without get damaged. Compatible Model Apple Watch Series 4 & 5 44mm.