Abstract: A device for supporting an object such as a dental x-ray unit on the free end of a vertically pivotal arm, which allows the object to be counterbalanced for stabilized vertical positioning. The supporting device includes a rigid tubular encasement having a pair of articulating knuckles pivotably attached at each end of the encasement, and a counterbalancing mechanism disposed within the encasement and connected at each end to the articulating knuckles, the counterbalancing mechanism including a compression spring having a force adjustment means, a rod disposed through said spring which includes a threaded fastener which engages one end of the compression spring, and linkage arms at each end connecting the rod to the articulating knuckles. The device is characterized by a readily accessible spring tension adjustment allowing job site adjustment to compensate for spring fatigue, improved efficiency and reduced costs resulting from a reduced number of operating parts, and improved operability.