Bike bells generally look sound a bit ugly but why what if they looked sexy sounded like an angel playing a glockenspiel the bells fit on almost all cylindrical bars the small oi is best for the common 222mm bar and with the spacers that come in the pack the large oi is for all bar sizes up to 318mm the oi will also work on any aero bar with a 16mm cylindrical section usually near the stem specifications size small bell fits bars 222mm diameter large bell fits bars 23