If you need to replace the small bearing and groove washers on your Positioning Arm this is the kit.  Kit includes one bearing and two washers.  These are fiddly little parts so relax and sit down in a comfortable chair with your Positioning Arm on a table in front of you.  These assembly photos should help.  A drop of oil on this bearing and in the Knob make the Positioning Arm lock up 2x as tight.