The balance arm mounts on the ceiling of the modular test cage or hubs. They are used to carry electrode leads, catheters, swivels and commutators. The balance weight on the arm may be moved as a counterpoise and locked in place.  The mounting holes in the mounting bracket of the balance arm aligns with holes on the ceilings of the test cages and hubs.  Two thumbscrews are included with the balance arms for securing the balance arm to the ceiling of the test cage or hub.