608-2RS Deep Groove Single Row Ball Bearing.
Inner Diameter: d = 8mm
Outer Diameter: D = 22mm
Width: B = 7mm
Material: Chrome steel GCr15
A very common size of bearing, often referred to as a roller skate bearing.
This size is used in many designs of Reprap
The 2RS designation is for rubber side shields. These have higher rolling resistance than ZZ style but offer better protection from dust and moisture.