Highly recommended for high speeds and quiet operation. These bearings are one of the most cost effective ways to increase roller service life. The radial ABEC bearing is assembled in the outer housing for easy installation. The adapter eliminates metal-to-metal contact between the bearing and axle which reduces noise during operation. Metal shields on the internal radial bearing prevent dirt and debris from entering the bearing without creating rotational drag. Not affective against small particle dust. Light oil further reduces rotational drag but is not recommended for powered applications. Recommended for gravity applications that require low noise and long life.