V-Share Adult Ajustable Bike helmet in Yellow1.head Circumference 56-63cm and the Head-width Below 17.5cm.please Check the Size Before Buying rashworthiness, not brittle to withstand the high intensity, strong foam density. Ultra-light, wind tunnel, duct design, effectively reduce wind resistance. High-quality foam layer, the adjustment within the twist, you can adjust the size of head circumference. Suitable for people with head circumference 58-61cm and the head-width below 16cm. Snap on/off visor for sun protection