Classic Aeron Lumbar Support Kit When installed properly, the lumbar support pad adjusts vertically to provide back support over a four-inch range, supporting the natural curve of your midback, or lumbar region. The pad can be positioned with a thinner or thicker side facing you to vary the level of support provided. This lumbar support kit increases the immediate comfort of the chair for those who like to recline as they sit. To find the size of any Aeron chair or stool, stand behind the chair and feel for the raised dots under the top edge of the back frame. One dot is the A (small) size, two dots in a row is the B (medium) size, and three dots in a triangle is the C (large) size.