The single rack roller kit comes with one axle/clip and one wheel/roller. The rack wheel is designed to allow the rack of your dishwasher to roll in and out. If the rack will not complete this task, or you notice that your dishwasher is not cleaning dishes properly, you may need to replace the rack wheel. The single rack roller kit is made of plastic, and clips to the dishwasher rack with the included axle/clip.