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First, just to clarify, item # ALESW581818BL is only a box of two replacement shelves, not an actual storage unit. The full Alera® Wire Shelving Units are available here.
You can add Alera Casters For Wire Shelving to the Alera shelving units. They are item# ALESW590004 and available here. Please note that adding casters reduces the load capacity of the shelving units from 4,000 - 5,000 lbs. to 2,400.
CT is an abbreviation of carton. Alera® ALESW584818SR Industrial Wire Shelves are sold by the carton, with 2 shelves in each carton.