Replacement Herman Miller Aeron Arm Adjustable Hardware. OEM Herman Miller Aeron Adjustable Swing Arm Thumbwheel Screw Assembly Arm Bolt. Herman Miller Aeron Adjustable Swing Arm Thumbwheel Screw Assembly Arm Bolt. OEM Replacement Herman Miller Arm Adjustment Hardware – 1 Piece (Arm). Part Number – 241715-G1. (Part #44 on the Parts Image Attached). See picture of what is included. 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®.