Grab rings

A grab ring comprising a substantially flat annular element having one set of teeth projecting outwardly from an outer periphery of the element at an inclined angle to the annular element to one side thereof and a second set of teeth projecting inwardly from an inner periphery of the element at an inclined angle to the plane of the annular element to the other side thereof to engage a pair of inner and outer concentric cylindrical surfaces to permit relative movement between the surfaces in one direction and to prevent relative movement between the surfaces in the opposite direction, the first and second sets of teeth substantially arranged directly opposite to one another and being radially spaced apart a distance equal to the width of the flat annular element.