Metallurgical ContentBall Mill TRUNNION BEARINGSTrunnion BRONZE BUSHINGSTRUNNION BASE AND CAPBall Mill LUBRICANT JACKSBall Mill PINION SHAFT BEARINGS The first part of the mill that we will look at is the TRUNNION BEARING. This is a HYDROSTATIC BEARING which is a slow moving bearing that carries a heavy load. Usually it is constructed from Babbitt’s metal.