Miracle Caster! Extra Large Chair Wheels. Set of Four. Great for carpet. Replaces chair mat 7/16" x 7/8" stem. These large chair casters roll more easily over carpet eliminating the need for a chair mat. Heavy duty. Guaranteed not to fail when used on carpet. (See details below.) Great for heavy individuals, people with mobility problems, or people who need a higher seat. Caster stem is 7/16" diameter. See photos above and description below for other dimensions. Sized to fit many office chairs but measure your current caster stem before ordering.