Lubricated at manufacturer for no additional lubrication required Metal on both sides of the bearing to keep lubricant in and contaminants out Chrome steel for durability and resistance to deformity under heavy loads Deep groove geometry for high speeds and supporting both radial and loads This 604ZZ 4x12x4-millimeter shielded miniature ball bearing has deep groove geometry for high speeds and supporting both radial and loads. Its chrome steel construction makes it and to deformity under heavy loads., Manufacturer: Akfldms