Normally part of the moulded wheel or a nylon bush may have been inserted so the wheel will run directly on a shaft or axle. Ideal for small load capacity applications.
Needle Roller Bearings
A cage holds steel roller together (needles) this will be found in the bore of wheel measure as the final required bore. Needle roller bearings will reduce friction between the axle or shaft and the wheel.
Precision Steel Balls encapsulated in a steel cage will reduce the friction between the wheel and axle of shaft – best suited for very high loads.