This bearing is sold to replace the bearing on the Monolithic Mixer. It is a sealed bearing that is designed to last through the tough conditions of mixing concrete. The ML1 and ML2 models of the Monolithic Mixer also have a inner seal that helps keep the cement water away from the bearing.
The key for long bearing life, is to not over grease it. Its a sealed bearing, that only needs to be greased once every 50 yards. When greasing the sealed bearing, just squeeze the handle on the grease gun very slowly, the moment you feel any resistance, stop. They typically need a 1/4 or 1/2 of a squeeze upon greasing.
Click here to see a video instruction on changing the bearing