Outside Diameter is 2 1/4"; Inside Diameter is 1 13/16".

This is a New Old Stock vintage set of 4 round casters.  Stock #6843.  Back of package advertises these are made of Acetate - a new revolutionary material that cannot break, chip or crack!  Protect floors, rugs and carpets from marks and stains, scratches and dents.  Unaffected by cleaning compounds.  Gives the utmost in protection.