Genuine Herman Miller Aeron Spider Base w/ Casters Wheels Swivel Chair. Came from a Size “C” chair. (I understand that it will fit Size B as well). All Genuine Swivel Spider Base and Casters Wheels from Herman Miller AERON Chair. Comes EXACTLY as shown. Excellent condition – will clean up to be nearly “AS NEW”. The chair this came from was assembled on 7/18/1997. It had little use.