This bike adaptor is designed to be mounted to a bicycle handlebar or seat post between 22 and 30 mm in diameter.Compatible with Tikkina, Tikka, Bindi, Actik, Actik Core, Tactikka, Tactikka + and Tactikka +RGB headlamps, it turns your headlamp into a bike light, so you can be seen. Note: Warning: when used in an area governed by traffic regulations, Petzl lights are no substitute for required standardized lights. Petzl Headlamp Bike Adapt