CUSTOM ADAPTATION PURPOSE: To make a powered wheelchair shorter for use under existing tables. Replace the existing front casters with roller blade casters and the rear drive wheels with smaller drive wheels. DIMENSIONS: The front casters are 4 inches in diameter (104 millimeters) and the replacement rear wheels are 8 x 3 inches. WEB SITE: http://www.wheelchairmodifications.org. REF: Powerchair Quick Modification. Wheelchairmodifications can also be reached at 5533 A Pony Farm Drive, Richmond, VA 23227.