Abstract: A metal forming tool has a pair of jaws which are pivotally connected to one another. One of the jaws is provided with a channel which is part-circular in longitudinal direction of the channel and defines a part-circular arc in a plane passing through the channel normal to such direction. The other jaw carries a spherical or part-spherical element having a radius equal to that of the arc. When the jaws are closed, the spherical or part-spherical element makes line contact, or approximately line contact, with the channel in a plane perpendicular to the longitudinal direction of the channel.