Spin Action Fit, offers maximum adjustment, fits head size 52-58 cm Side-squeeze buckle for easy adjustment 21 vents Tapeless Technology CPSC 1203 Bike Compliant Designed for the road, or the road less traveled, the Bell Cadence is the ideal choice for road rides and joy rides alike. Its compact profile and 21 large vents keeps you cool as you cruise, while the easy one-handed adjustable Spin Action Fitsystem gives you unbeatable comfort. No matter how fast or how far, the Bell Cadence is the perfect partner for your ride