Airius Bicycle helmet. 18 vent design allows great air flow. Dial adjustable rear headlock system. Removable visor. CPSC approved. Nice light weight well fitting helmet. Be safe! Red, Blue, Wht. Measure the crown of your head the Small/Medium will fit head sizes between 20-3/8th and 22-3/4". The large fit sizes between 22" and 24". Please note that the larger size will fit most adults. The Smaller one is a great size for kids age 3-8.