There are two types of bearings used in a trunnion: ball bearings and roller bearings. Ball bearings are used in most applications. They are cheaper than roller bearings, but they do wear out over time. Roller bearings are usually used in higher-end machines where there is less friction. If you're replacing a trunnion bearing, you'll need to remove the shaft first. To remove the shaft, loosen the nut holding the shaft in place and slide the shaft off the trunnion. Next, use a socket wrench to remove the old bearing. Use a new bearing and tighten the nut back down. Replace the shaft and reassemble the trunnion. You're done!