A bearing block structure for an implement rockshaft includes a two-piece ultra high molecular weight (UHMW) polyethylene wear insert located between a cast iron or welded steel bearing block and a rockshaft. In one embodiment, identical insert halves are supported in corresponding insert cavities in the bearing block sections, and a small thin clip is secured between the sections to prevent relative rotation between the insert halves and the bearing block. In another embodiment, a stop member projects into the cavities to prevent rotation of the insert halves.