The Daymak SB-103 bicycle helmet is the safe and comfortable way to ride around on your bicycle or ebike. The SB-103 helmet is CPSC and CE EN-1078 certified ensuring the effectiveness of the protective head gear. The 10 air vent keeps your head cool while its aerodynamic shape provides little air resistance while riding. The adjustable quick release clip makes adjusting how snug the helmet is easy and taking it on and off a snap. These helmets are great for children and adults. Sizing Chart: Small (54 – 56 cm) Medium (56 – 58 cm) Large (58 – 60 cm) Extra Large (60 – 62 cm).