Several mills on the pacific coast of the U.S. are currently running tests on a new kiln cart bushing. These were designed by Redwood Plastics’ Woodland location in response to complaints about existing bushings in the mills. The regular blue nylon was causing frustrations as the kiln carts were difficult to move. To the point that, in at least one case, machinery was needed to push/pull the carts. 
The new bushings made of nylon PVM or “Pressure Velocity Maximum” have performed much better. The carts slide easily and the safety yellow coloring (to differentiate from the standard nylon bushings) has also been applauded. For more information check out the original blog posting here.