Popular light- and medium-duty FAULTLESS Casters are used everywhere—home, office, and industry. Cold forged raceways with hardened steel ball bearings. Single ball race recommended when swiveling efficiency is not important and done infrequently. Single ball race is included on models with 2"Hx7/8"W and 3"Hx1-1/4"W wheels. Double ball race, on all other models, is for smoother, quieter swiveling, and when item is turned often. Wheel type codes are:Semi-steel (SS)Soft rubber (SR)Hard rubber (HR).