The roller bearing allows the roller to move freely around the axle.  Bearings come in a number of different styles, materials, and qualities.  Standard bearing options for Gravity Roller conveyor include:

NON-PRECISION, OIL: Bearings are made to rather loose tolerances with lots of clearance between inner and outer race. Lubricant used in bearing allows free - wheeling of the roller. It provides the most "lively" rollers. It is not desirable under driven conditions, or in powered roller applications because the lubricant doesn’t hold up to these conditions. These rollers are normally adequate in environments up to 350 degrees F.

NON-PRECISION, GREASE PACKED: Bearings are made to rather loose tolerances with lots of clearance between inner and outer race. Greased lubricant is primarily used in driven roller applications.

SEMI-PRECISION: Rough machined inner and outer raceways. These bearings have ball retainers, separating the balls, providing for more loading and holding up to more severe applications than non-precision. The ball retainer prevents operating temperatures over 150 degrees F.

PRECISION: Ground components, including inner and outer race and balls, are carefully fit together with tight tolerances to make high quality bearings capable of holding up to high revolutions per minute and high loads. Ball retainers separate ball bearings; typically the bearings have shields to keep debris out, therefore they are better in harsh environments.