I believe it's called a steering dampener. At 19,000 miles I replaced mine yesterday along with an oil change. Today after my commute to and from work round trip of 115 miles I can say it was well worth the twenty bucks. It did not completely eliminate the trammeling or truckers rut but it is a big improvement. The over all general feel is just much better. Driving over small imperfections on the road transfers much less vibration to the wheel.
Bill,