Yukon Gear & Axle Spin Free Kits increase fuel efficiency and reduce maintenance costs. The kits replace the failure prone and expensive factory unit bearings with tapered bearings and races. The result is not only a design which is easier and more economical to service, but one that offers significant increases in fuel efficiency because there are fewer rotating parts in the drivetrain. Less work equals more mpg. These hub conversion kits also include low-profile Yukon Hardcore Premium Locking Hubs, for quick changes between two-wheel and four-wheel drive.