Grayne Black MTN Ski & Snowboard Helmet w/Outdoor Tech Audio Built in Goggle channel and Retention Strap Outdoor Audio Tech Wired Audio Chips On the fly adjustable venting Twist-to-Fit Dial System Simply twist the dial on the back of the liner to find the perfect combination of comfortable yet snug. The innovative harness design matched with the Twist-To-Fit Dial System allow the MTN to fit an unparalleled size range with the Medium comfortably accommodating head sizes from 54-59 cm and the Large fitting 59-64 cm! CPSC and EN 1077 certifications ensuring that the MTN will provide maximum protection!