This replacement support pad is used for the Aeron Classic chair. 

It is one size for all Aeron black classic chair (size A, B,C)

This item does not include screw. When you are removing the old support pad from your chair, you will need to keep the original screw to connect the new pad. 

This product is from third party not from Herman Miller.

Please contact me if you have any question about the product and delivery