This is the Hitec Universal Ball Bearing for Servos.

FEATURES: Constructed of steel

INCLUDES: One ball bearing for servo

REQUIRES: Installing onto servo

SPECS: Outer Diameter: 10mm Inner Diameter: 6mm Thickness: 2.5mm  

BOX DIMENSIONS: 3.00" W. X .13" H. X 5.25" L. BOX WEIGHT: .01 LBS.