Size for the helmets would be :XS: 53-54 cm, S: 55-56 cm, M: 57-58 cm, L: 59-60 cm, XL: 61-62 cm basis head measurement. Kindly refer image size chart for details.- the dual EPS liner of a helmet is designed to fit the head perfectly to absorb the energies of an impact and avoid penetration. The chinstrap secures the helmet and the head in order to prevent them from rolling. Double D-ring for a secure fit- Upper air intake vent is positioned to maximize air volume into the helmet interior, Back outlet vent is integrated with pc spoiler, allowing it to be positioned for optimum flow-through ventilation, Breath guard and chin curtain included- Optically correct visor equipped with pin lock system, Quick and toolless visor change mechanism, Internal sun visor included- Integrated Spoiler for Streamlined Presentation & Stability at High Speedmade with tough polycarbonate material