?Suitable for caliber?This Airtag hidden bike mount is suitable for all mountain bikes with fork lower bore inside diameter from 18mm to 30mm. Configured with four different sizes of expander brackets, there is always one for you, feel free to ask questions. ?Securely mounted, not easy to fall off?The retractable bracket is a two-way retractable fixed lock, you don't need to worry about the natural inertia to fall off when using, very safe and secure to use. ?Hidden Anti-Theft Design?Airtag bike mounts are hidden in the most inconspicuous place, mounted at the bottom between the front wheel and fork, unnoticeable, perfect for preventing your bike from being forgotten and tracked by theft. ?Package Contents?1x AirTag bike mount, 2 x reinforced nylon cover, 2x EVA protective pads, 1x expander mount 18-20.9mm, 1x expander mount 21-23.9mm, 1x expander mount 24-26.9mm, 1x expander mount 27-30mm, 1x M3 wrench, 1x M5 screw and a screw cap. (AirTag Not Included). ?Product Specifications?Product weight:98g, Package size:8.2*8.2*3.2cm, Product material:Aluminum alloy + plastic.