Premium Racing Bearing use high temperatures oil type for high-speed rotation and realizing a maximum lighter drive train.
Their special construction with a protective black rubber seal on the outer side and a super low-friction steel inner shield on the side maximum protection against the elements while optimising the drive train efficiency compared to all-rubber shielded ball races. (DK-10503ZZ is metal shielded)
Premium Racing Bearing makes them especially useful in demanding applications such as all category.