DW SM-9212 Closed Hi-Hat Boom Arm If you've ever needed to put a closed hi-hat into a tight space, you'll instantly appreciate the DW SM-9212 Closed Hi-Hat Boom Arm The DW SM9212 is 1/2"x18" If you've ever needed to put a closed hi-hat into a tight space, you'll instantly appreciate the DW SM-9212 Closed Hi-Hat Boom Arm The DW SM9212 is 18" x 1/2"