This is a replacement 37-tooth ring and 13-tooth pinion gears for front differentials.Replacement part for these models:Ford® F-150® Raptor R™ 4X4Ford® Fiesta® ST RallyHoss® 4X4 VXLRevo®Rustler® 4X4 VXLSlash 4X4 UltimateSlash 4X4 VXLSlayer® Pro 4X4Stampede® 4X4 VXLSummitT-Maxx®XO-1®Accessory part fo..