Geared PRT slewing rings replace ball bearings and other rolling elements with sliding elements made of low-friction, self-lubricating polymer. A toothed belt mounted on the bearing’s inner or outer ring is driven by a sprocket. The ring module arrives ready to install.The rings come in plastic, aluminum, or stainless steel. The sliding pads are iglide J, which has a low coefficient of friction, resists chemical exposure, absorbs little moisture, and damps vibrations. There are no minimum order requirements, and custom bearings are available. igus, P.O. Box 14349, East Providence, RI 02914, (800) 521-2747, www.igus.com