Deep groove geometry for high speeds and supporting both radial and axial loads Chrome steel for durability and resistance to deformity under heavy loads Metal shields on both sides of the bearing to keep lubricant in and contaminants out Lubricated at manufacturer for no additional lubrication required This 604ZZ 4x12x4-millimeter shielded miniature ball bearing has deep groove geometry for high speeds and supporting both radial and axial loads. Its chrome steel construction makes it durable and resistant to deformity under heavy loads. Material: Bearing Steel Color: Silver The metal shields on both sides of the bearing keep lubricant in and contaminants out, and it comes pre-lubricated from the manufacturer so that no additional lubrication is required. This deep-groove shielded miniature ball bearing is for use in applications that involve combined radial and axial loads and a need for high running accuracy at high rotational speeds. Such applications include clutches, drives, gearboxes, compressors, pumps, turbines, and printing and textile machines, among others. Rolling bearings use rolling elements to maintain the separation between moving parts to reduce rotational friction and support radial and axial loads. Sealed bearings are lubricated with oil or grease in the bearing factory, while open and shielded bearings are meant to be lubricated in place, with periodic reapplication of lubrication, based on use. The shield protects the working parts of the bearing from environmental debris that may be introduced and could reduce the ball bearing speed and lifespan. Rolling bearings are used in a range of applications from agricultural machinery to conveying equipment, robotics, dental equipment, elevators, rolling mills, rudder shafts, and aggregate crushers, among others. Package Contents: 20 x Deep groove ball bearings Only the above package content, other products are not included. Note: Light reflection and different displays may cause the color of the item in the picture a little different from the real thing. The measurement allowed error is +/- 1-3cm.