Replacement Herman Miller Aeron Chair Pneumatic Cylinder Height Tilt Kit + Lever and Cable. OEM Replacement Herman Miller Aeron Chair Pneumatic Cylinder Height Control Lever Tilt Kit and Cable. MEDIUM SIZE C CHAIRS. Aeron Fit / Size Chart. How can I determine my chair size if the label is gone? – To determine the size of your chair, feel underneath the top back lip of the chair’s backrest for a number of bumps. 1 bump is A, 2 bumps are B, and 3 bumps are C. One can also measure the seat pan width: Small A is 19 inches wide, Medium B is 20.25 inches wide and Large C is 21.5 inches wide. We accept most major credit cards in our showroom. The Original AERON® Chair. Herman Miller Mirra® Chair. Herman Miller Embody® Chair. Herman Miller Sayl Chair®. Herman Miller Setu Chair®.