These 1/8" thick clear Poly-carbonate quarter windows are direct replacements for the 997 CUP Porsche with the addition of a NACA duct. They are ideal in race car builds where you need to get additional air into the engine for cooling or the cabin for the driver. The Naca duct placement is just behind the factory installed cage on 997 GT3 CUP cars and is designed to fit a standard 3" hose. These windows come with the pre-drilled hole for standard installation in CUP cars. Quarter windows are sold in pairs.