This arm allows for mounting of a possible 4 heads – 2 on the sides of the arm and two perpendicular to the arm. There are two 1 4 -20 mounts (1 on the end and 1 on the arm) and two 3 8 mounts (1 on the end and 1 on the arm). The Studio Assets Cross Arm also comes with an adapter which can turn a 1 4 -20 to 3 8 allowing for several different mounting options. The Cross Arm Assembly is the perfect accessory for creating a robust workstation. The Cross Arm makes it easy to attach Cameras, Video equipment and laptop trays to a tripod or camera stand.