BassForms BF212GM99 Dual 12" Custom Fiberglass Enclosure for 1999-2006 Chevrolet Silverado/GMC Sierra Extended Cab Trucks (fits square & round cut out &gt; Ex. Kicker 12" L3, L5, & L7) Dual 12" Custom Fiberglass Enclosure Vehicle specific for 1999-2006 Chevrolet Silverado/GMC Sierra Extended Cab Trucks Designed for louder, deeper bass Custom looks & form minimizes trunk junk: Lightest, most durable boxes on the market Airspace: 2.08 / Speaker Depth: 7.1