These 1/8" thick clear Poly-carbonate quarter windows are direct replacements for the 997 CUP Porsche and include the factory style slots that allow air to escape the cabin of the car. They are ideal in race car builds where you need to get the air out of the car to prevent buffeting and to provide air flow. They come with the pre-drilled mounting hole standard in 997 CUP installations. Quarter windows are sold in pairs.