This is an authentic Milwaukee replacement part. The ball bearing is designed by the manufacturer for use in drills and sanders. This part is made of metal, and is generally used to allow a shaft to spin freely. It may be found in different locations in the machine, depending on model. Please be aware that there are different ball bea...Read morerings used in the machine. Refer to the parts diagram to be sure of ordering the correct part. You may require an Allen wrench or screwdriver when replacing this part. This item is sold individually.