The AT3.0 / 4.0 Visor Kit is a full set of replacement parts for the visor mechanism of your AT3.0 or 4.0 helmet. The kit includes the sprung mechanism, the mechanism cover, and the bayonet thumbscrews that secure the visor into the mechanism.SizingFor AT4.0 sizes XXS to XS, choose visor kit size XS-S. For AT4.0 sizes SM, choose visor kit size M. For AT4.0 sizes ML to XL/XXL, choose visor kit size L-XXL. For AT3.0 choose the size range of visor kit that correlates to your 3.0 helmet.