This includes the two main parts of the adjustable arm, thumbscrew, plastic washer, and rubber washer for the Atlas Extra Tall support.
This arm is the only difference between the Atlas Tall and the Atlas Standard or Atlas Short. If you have a Standard or Short, you can purchase this arm to convert it to a Tall.
I needed my position a little higher. This longer arm fixed that just fine. My only critique is that a hex wrench should be included. Otherwise, it was simple to install and worked well.