1. Material: aluminum alloy + plastic 2. Waterproof design, can withstand various weather conditions and protect your equipment 3. Aluminum alloy bell surface, ringing sound is clear and loud 4. Compact and mini, it takes up no space and is effortless to carry around. 5. The tracker can be placed in the bell to find the bicycle at any time. The hidden design makes it difficult to be discovered. 6. The 5th generation is suitable for 20-35mm pipe diameter, and the 6th generation is suitable for 10-40mm pipe diameter. 7. Note: Bell only, tracker not included