Bronze SAE 841 is particularly noteworthy because it is a powdered metal. These are a special class of materials designed to be used in bearings. Where most of our materials are cast or wrought, powdered metals are first cast, then ground down into powder. This powder is then combined with oil and a binding agent and compressed under high heat to make a shape, typically round rod or hollowbar. Roughly 19% of the volume of the material is SAE 30 weight oil. As a machine using this bearing comes up to speed and temperature, a fine layer of oil sweats out of the bearing and coats the shaft, providing self-lubrication. When the machine is turned off and the bearing cools, capillary action within the bearing acts to absorb the oil back into the metal.