Calumet CK7981 Horizontal Cross Arm Assembly Bar for Mounting Multiple Flash Heads or Cameras to Your Tripod This handy horizontal cross arm can be used to mount multiple flash heads or cameras to your tripod or stand for a variety of functions. The cross arm mounts to any column with a 3/8 thread and allows for up to two flash heads or cameras or a combination of one of each to be attached to its two horizontal sliding mounts. The cross arm can be used for a variety of purposes It will hold up to four flash heads for multiple flash setups. Each sliding mount features a 3/8 thread.