Gibraltar SC-RMAA Rack Tube Mount Adjustable The SC-RMAA Rack Tube Adjustment Boom Attachment is adjustable size and fits over any 1 1/2 inch diameter rack tube and allows mounting 3/4", 1/2" and 7/8" diameter cymbal, tom, and accessory arms via adjustable sized insert Fits over any 1-1/2"-diameter rack tube and allows mounting 3/4", 1/2", and 7/8"-diameter cymbal, tom, and accessory arms Fits over any 1-1/2"-diameter rack tube and allows mounting 3/4", 1/2", and 7/8"-diameter cymbal, tom, and accessory arms