604UU Type Ball Bearing. This bearing is unique in that the bearing face is concave or ‘U’ shaped. It was designed primarily to be used on linear rail systems. This bearing is similar in profile to matching the linear rails found on the Z axis of the Formbot T-Rex and Raptor 3D printers. 

Dimensions:

Outer Diameter: 13mm

Depth: 4mm

Inner Diameter: 4mm

 U604ZZ SZU4-13 604UU U groove deep groove ball bearing