3 Lever Herman Miller Aeron Mesh Office Swivel Chairs. Ergonomic Size B   Black/Grey 2 available. I do have very similar ones 

These Chairs are considered to be one of the best chairs on the market.

The Herman Miller chairs are in a good condition minor marks only. Read up on chairs and see the outstanding reviews 

They are Height Adjustable. And have 2  seat tilts front and back  the arms are adjustable up and down. And move in and out, big for comfort. And with Tension  control The chairs are built for maximum comfort. Built in lumber support on the back with an added Adjustable Lumber back pad . Mesh back and seat. Brilliant chairs at a good price