Herman Miller Aeron Chair Replacement Seat Pan Graphite Medium Size B Frame. NEW Replacement Herman Miller AeronSeat Pan – Parts only – No Chair Herman Miller Aeron Chair OEM Replacement Seat Frame Pan Graphite MEDIUM Size B241724-G1-PurpleSeat Pan Size B Graphite – NO CHAIR IS INCLUDED 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. ONLY FOR THE CLASSIC STYLE AERON – Not the Remastered Version. Check out our entire store for more great products and deals! We do however make every possible attempt to accurately describe the inventory we sell and stand behind it. Since 2016, 8TEN Industries has been a leading asset recovery provider supporting national retailers, brands, and manufacturers. Our 60,000 square foot processing and distribution facility located in Cass City, Michigan has allowed us to become industry leader in turning difficult problems for manufacturers into great deals for our customers.