Probe and the magnet should be a 2mm sensing range, within the handlebar diameter 2.5CM Stopwatch Specifications: High: 5.1cm Width: 4.6cm Thickness: 2cm * Model: YS-368C Type: wireless-type 15-function Material: plastic electronic components * Show: LCD display Color: Black Battery: CR2032 (batteries not included) * Includes: 1 x Wireless LCD Bike Bicycle Odometer Speedometer 1 x Mounting Shoe * 1 x Sensor 1 x wheel Magnet 1 x Cable ties 1 x User Manual