Inspired by the aggressive lines of ba terrain, the Oakley mod5 is geared toward the technical adventure enthusiast. The mod5 has a hybrid shell design that provides increased protection to common high-impact areas. It also features a modular brim system (mbs) that redefines seamless helmet and Goggle Integration, while also aiding in Goggle anti-fog performance by funneling hot, humid air out of the Goggle and through the brim of the helmet. The mod5 includes a boa closure system securing the helmet fit with 270 degrees of adjustment, a fid lock magnetic buckle providing the convenience of one-handed use while wearing gloves, and an optional mips rotational protection liner for brain protection. The mod5 delivers the perfect balance of premium functionality and increased protection, giving you the confidence to find new boundaries. Sizing: small = 51-55cm medium = 55-59cm Large = 59-63cm mbs Goggle compatibility: small brim = a-frame 2.0, crowbar, open-frame 2.0 XM, open-frame 2.0 XS, e-frame, wind jacket 2.0 Large brim = airwave, airbrake XL , airbrake, Flight deck, Flight deck XM , canopy, line miner & O frame 2.0 XL.