a flexible mandrel for use in bending tubes and especially for producing tight bends in thin wall , high strength metal tubing . the mandrel comprises a series of ball members each of which is adapted to nest within the preceding ball of the series as the mandrel is flexed . the balls are free to rotate transversely and to slide longitudinally on a series of rigid link members which are flexibly interconnected . the balls and links are so constructed that as the mandrel is flexed , each ball pivots around a point located at or near the geometrical center of its outer curved surface .