Miracle Caster! Extra Large Chair Wheels. 4" Set of Five. Great for carpet. Replaces chair mat. 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.