The Jeep NP231 is one of the most popular transfer cases, but it creates an extremely short rear driveshaft. These fixed yoke kits from Advance Adapters add 3 to 4 in. to the rear driveline length on a YJ, and up to 6 in. on a TJ. This results in a better driveshaft angle, eliminated driveline vibrations, and a transfer case that's ideal for trail use.