This is an Genuine Manufacturer Authorized replacement part used on variety of power tools. Ball bearings are used to reduce friction between rotating parts. The balls or rollers take the load and spin, distributing the weight evenly while the minimal contact area of the ball reduces friction. This reduces wear on the tool and allows it to run smoothly. Bearings experience constant wear when the tool is in operation from pressure, heat, vibration and friction. Because of this, many Bearings need periodic maintenance or replacement.