What caster upgrades are available for ergonomic chairs?

Caster upgrade specification at OfficeFurniture2go.com: hard floors require soft-roll polyurethane (80A Shore hardness), carpet requires standard nylon, heavy-duty users require 75mm diameter for load distribution. All commercial chairs we sell use the 7/16\" universal stem — straightforward tool-free replacement. We specify and stock casters for every chair in our catalog. Call 1-800-460-0858.