With the LD Systems LDICOAPROSUB21CB castor board, the ICOA PRO SUB 21 A can be conveniently transported to any position. The 21" High-Performance Subwoofer is securely fastened by two integrated butterfly fasteners. The stackable castor board made of 0.7" (18mm) multiplex runs on four 3.9" (100mm) heavy-duty castors and is optimally protected from scratches and other signs of wear by its polyurea coating.