608ZZ 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 ZZ designation is for metal side shields. These offer lower rolling resistance than 2RS style but less protection from dust and moisture.