The Perimeter Seal system is the latest technology from Racing Optics which allows for a tighter seal to the visor, blocking out dirt, dust, and water from behind the tearoff stack. The laminated technology creates a distortion-free optical lens. The XStack is a stack of 10 laminated tearoffs that are 2mm thick each. Each package contains 3 stacks of 10 tearoffs for a total of 30 tearoffs. These tearoffs feature large tabs for dirt racing. Cannot be used with the Zylon Visor Panel. Compatible with the RS7C LTWT, RS7SC LTWT, RS7 Carbon, RS7 Pro, RS7-K, HP7, KC7-CMR Carbon, and KC7-CMR.