Use to add aftermarket speakers to factory door locations. Slight modification of the speaker adapter is required for some speakers- that's normal and that's why these fit so many different sizes. Made specifically for most 5.25", 6", 6.5", and 6.75" speakers. Speeds up installation time. Made from high grade plastic for a long lasting secure fit and corrosion resistance. 2 pair each for 4 doors- 4 plates. Compatible Vehicles: Made for Chevrolet: 2002–2009 Trailblazer; Made for GMC: 2002–2009 Envoy; Made for Oldsmobile: 2002–2004 Bravada