Bern 2016 Men's Macon EPS Summer Bike Helmet w/Crank Fit Head Size: 54 - 57 cm Thinshell EPS foam with ABS outer shell gives a durable and long lasting, low profile fit. Crank Fit dial on back of helmet quickly secures or loosens the fit around your head, super easy to adjust - even on the fly. Meets Safety Certification ASTM F 2040, CPSC and EN 1078 and WINTER UPGRADE KIT AVAILABLE SEPARATELY