Abstract: A mechanical concentric support device for use on machine tools such as lathes, precision grinders and the like, for either internal or external engagement of the workpiece by radially extensible support shafts driven by a scroll mechanism. The key connection for the scroll mechanism is located on one of the circular faces of the device to permit close-fitting internal support of cylindric workpieces, and adapters are shown for both internal and external gripping of workpieces of a wide range of diameters both larger and smaller than the diameter of the support device.