lightly cleaned vintage american industrial cast iron and steel "adjustable supporter" or knuckle joint, first patented by otis c. white in 1893 for use with electric lamps or lighting used in factory and/or various commercial settings. the compound swiveling, sliding and clamping joint was designed in part to connect primary and secondary tubular steel arms of an articulating lamp or light fixture. in addition, the joint provides longitudinal and rotative adjustment of the secondary arm in all directions relative to the primary arm. the brushed cast iron and steel joint consists of a swiveling head having an adjustable grip and clamping jaw for securing the lamp arms (i.e., primary and secondary). a swiveling head is fitted to rotate on a suitable seat on the main part of the joint, and is axially retained by a pivot or screw that passes through the parts. the pivot includes a circular head located in a cavity within the swiveling head. the pivot is non-rotatable in the main part of the joint, and a nut or binder is fitted on its opposite end outside the clamp jaw, so that by tightening the nut, the multiple parts can be clamped together with sufficient friction for retaining the lamp's arms at any desired angular position. a yielding washer is typically utilized between the nut and jaw to render the action more efficient and satisfactory than would rigid clamping of the parts. a threaded grip diminutive set-screw is employed for adjusting the pressure of grip on the adjustable arm. the fully functional components have been lightly cleaned. limited quantity of knuckle joints available. priced individually. measures approximately 1 1/2 x 2 x 3 inches.