The size is 8.5 inches (6-lug). Gear ratio: 3.73 (considered one of the best and strongest ratios for acceleration torque, and highly sought after by those who modify or love the truck's torque in the desert and drag races). Compatible vehicles (direct fit): - GMC pickup trucks: GMC Sierra and Chevrolet Silverado 1500 (models 1999 to 2006, and 2007 Classic). - GMC SUVs: Yukon, Tahoe, Suburban, and Yukon XL 1500 (models 2000 to 2006). (Note: The differential housing, axles, and size perfectly match the SUVs, but the buyer may need to transfer the leaf spring/coil spring mounts according to their vehicle). If the leaf springs fit directly, the sale is final.