Nitro's pro level racing bearings - X-7 Ceramic - feature removable delrin seals.  Manufactured by Khiro Skateboard Products for Pro Team Rider - Jason "Racer X" Mitchell - multi-time downhill slalom Pro World Champion - in the mid-2000's.  The Nitro X-7's are very high-quality premium bearings and come packaged in a hard plastic screw-top tube with additional stickers included.  Set of 8 bearings - enough for four wheels - one skateboard