Abstract: An over-center self adjusting cap chuck adapted for operative attachment to a high-speed capping machine includes a housing having an outer peripheral surface defining an inner annular periphery with an interior face. A plurality of independent engagement jaws are aligned along an annular area of, or within a pocket area of, the interior face. Each engagement jaw has a fastener to connect the engagement jaw to the housing and establish a pivot point to support a limited axial rotational movement thereof to a first open axial position and a second closed axial position for receiving and gripping a work piece respectively. Either a singular bias spring or a pair of bias springs pre-dispose the engagement jaws to the first open axial position.