Brass: bell for clean sound. 360 degree dinger rotation. High fatigue spring. Fits bar diameters 22.3mm - 26.0mm. Flexi: The Courtesy Flexi bell gives you the flexibility to mount it on handlebars of any diameter and other locations such as your stem. Its diminutive size and clean tone make it a great way to announce to other path users that you are passing on the left. Clincher: The beauty of this little bell's unique design is that it securely attaches to your bike's cable housing so it doesn't require any real estate on your handlebars. Mount it within reach of your thumb or forefinger and ring out a crisp "ding,ding, ding" when you merrily pedal past on the left.