A center bearing is the component of a torsion system that allows the torsion tube to spin within the mounting bracket, which helps support the tube across the top of the garage door frame.
Good: Plastic center bearings are a single donut-shaped component through which the torsion tube is placed. Because it is a fixed unit, the torsion tube may rub on the plastic center bearing and cause wear.
Best: Sealed steel center bearings are the same donut shaped piece of steel with a second piece of steel placed within the donut, supported by small sealed bearings for independent movement. The fluid movement of the second piece of steel eliminates friction on the tube for smoother operation.