Tripod Joint is used at the inboard end of car driveshafts, it enables power transmission even in case of angle shifting. Tripod Joint has needle bearing / barrel-shaped rollers mounted on a three-legged spider / three-pointed yoke, instead of balls bearings. These fit into a cup with three matching grooves, attached to the differential. The rollers are mounted at 120-degrees to one another and slide back and forth in tracks in an outer “tulip” housing.
Both axles got replace because the passenger side cv boot broke and went unnoticed until the bearings started buzzing so we decided to replace both of them to prevent from having to do future repair on the other one.