Abstract: A self-energizing lathe chuck is provided with a pair of interiorly mounted clamping shoes which serve to grip a piece of stock directed through an aperture in the chuck so as to retain the stock in a desired working position. The clamping shoes are mounted to a pair of pivot plates which rotate within slots provided in the chuck, and a spring is utilized to bring the clamping shoes into engagement with the stock so as to retain the same in a working position. A movement of the stock through the chuck in one direction results in the clamping shoes being released from engagement with the stock, while any attempted movement of the stock in the reverse axial direction is prevented by the engagement of the clamping shoes with the stock.