Required on Dana 30 front axles if installing an aftermarket ring and pinion having a ratio of 3.72 or numerically higher.0Fits Dana 30 Front Axles ONLY Fits 3.73 Ratio and Numerically-Higher R&P Gears2-3 hours1978-1986:4WD:Jeep:CJ;1997-2006:4WD:Jeep:Wrangler TJ;1987-1991:4WD:Jeep:Wrangler YJ