This is Novak's Ballistic Bearing Cap/Replacement Rear Bearing for the Ballistic 540-sized and Ballistic 550-sized motors. (#S5944). Drivers have the ability to choose between a steel (#S5943) or ceramic rear bearing (#S5946).
Each kit includes:
One Bearing Cap
One Rear Bearing (steel or ceramic)
One Sensor Grommet
Installation Instructions