Bicycle ball bearings all abouts, most of the Bicycle ball bearings have rubber seals to protect the bicycle ball bearings from dirt, dust or any possible contamination, Bicycle ball bearings are lubricated with grease, you can always remove the seals, relubricate the sealed ball Bearings with grease then put the seals back again. Bicycle ball bearings has item number ends with 2RS which stands for 2 rubber seal enclosures.