Bearing Type

Precision Sealed Ball Bearing 
Recommended for the product required high rolling ease and for medium duty to heavy duty loads, it is also no maintenance lubrication required.
Roller Bearing
Roller bearing is capable of carrying a greater load than the same size diameter ball bearing.
Combination seal washers protect the bearing from dirt, water, and chemicals.
(Note: Roller bearing must be used with steel outer shell for protection and add the rolling ability)
Plain and Sleeve Bearing 
Plain and Sleeve bearings provide a metal sleeve inserted in a wheel to rest directly on the axle. In addition to improve the load capacity, it will help provide the protection and support between the caster and axle. Only recommended for when rolling ease is less critical.