The critical interface between a car's steering rack and steering knuckle is the tie rod end. The rod end serves as a pivot point for the steering to retain its geometry in addition to transferring force from the steering rack to the wheels. The rod end normally has a round end and a threaded bolt that is put into the knuckle perpendicular to it. The rounded end also contains bearings that permit the bolt to revolve freely; a boot covers this end to prevent dirt from getting in. While this design may appear simple at first glance, the tolerances required are extremely fine because of how important it is to be handling.
