Enduro\'s ABEC 5 is the next performance step up from the popular ABEC 3 range. By using military level, high precision HRC-64 hardended Grade 5 Chromium Steel Balls, and 52100 High-Carbon Chromium-Alloy mirror polished races. This combination allows Enduro\'s ABEC 5 bearings to use tolerances twice as tight as ABEC 3, and operate without any noise. The Graphite/Nylon ball retainers allow virtually frictionless movement and provide constant lubrication to maximise the life of the bearing.Key Features: Bearing Code: 6903 (61903),Dimensions: 17mm x 30mm x 7mm,ABEC: 5,Grade: 5,Seals: SRS,Grease: Kyodo Yushi PS-2,Application: Hubs, Bottom Brackets,Weight: 15.86g.