FUSION IN-POLYCARBONATE SHELL – A process pioneered by Bell bonds the helmet s outer shell to the EPS foam liner to create a sturdier helmet. ACTION FIT – Designed for street and skate helmets, this streamlined fit system offers an adjustable, secure fit with the turn of a dial. RETENTION SYSTEM – Smartlock No-pinch Side Buckle. SPECIFICATIONS – Universal Toddler (45-51 cm) and Universal Child (57-54 cm) Sizes. Important: always take a measurement. Sizes and shapes can vary, even within an age range. Using a helmet that does not fit can be dangerous.