Enuff Black bearings: Ultra-fast precision bearings Removable rubber shields for easy servicing Precision clearances giving an ultra-smooth ride Low Friction Nylon Ball Retainer Chrome Bearings

Enuff bearings are high-quality and long-lasting; they provide smooth rolling and fast riding. Available in ABEC5, 7 and 9 as well as Swiss and Black versions. Standard skate bearings size which will fit all wheels including Skateboards, Scooters, Inline Skates, Quad Skates.

'ABEC' is the rating system that referes to the frictional load/spin.  The higher the ABEC number the faster the bearing is going to be. 

Note:  I personally use these bearings in all my skates and they are amazing, fast and smooth. (Russell AJ's Roller Disco)