The 250-55-21 or 2505521 Dana Spicer splined sleeve is a drive shaft part. It is the splined member of a driveshaft slip joint: it locks to the mating shaft so torque passes through, yet the two can slide along each other as the shaft needs to change length. Those sliding splines depend on grease, usually fed through a fitting, and on seals that keep dirt and moisture out of the joint. This is a genuine Dana Spicer part from Pro Gear and Transmission. Call us to confirm proper fit for your application.FeaturesDana Spicer drive shaft splined sleeveSplined member of a driveshaft slip jointLocks to the mating shaft for torque while sliding lengthwiseSliding splines rely on regular grease and sealed-out dirt and moistureGenuine Dana Spicer part sold by Pro Gear and Transmission