NEW Replacement Herman Miller Aeron Backrest. Parts only – No Chair. Herman Miller Aeron Chair OEM Replacement Backrest Frame Pan Graphite Frame LARGE Size C. 241730-G1 Backrest Size C – NO CHAIR IS INCLUDED. Aeron Fit / Size Chart. Use & Care Manual. Video Adjustment Information View these QuickTime videos to learn about the ergonomic adjustment options available on Aeron seating. Instructions shown are for all possible adjustments; specific adjustments vary according to chair model. 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. And in store payments. Items have no guarantee from Vitalityweb.