The Bell(R) Adult Primus Bike Helmet is suitable for all your rides whether commuting or taking across town adventures. The Primus is constructed with an in-mold polycarbonate shell for optimal safety and durability, and features large 17 vents for cooling ventilation and comfort. The Ergo Fit(TM) system is quick and easy to adjust, and ensures a secure fit with a turn of the dial. FEATURES: Best for road biking Sleek, compact shape Ergo Fit(TM) system features an easy-to-turn dial that provides an adjustable fit Ventilation: 17 vents In-mold polycarbonate shell and EPS construction Complies with U.S. CPSC Safety Standard for Bicycle Helmets for persons age 5 and older SIZING: Universal Adult Size: 54-61 cm / 21.25" - 24.01"