Abstract: To obtain a compact structure and to increase at the same time the structural stiffness of an apparatus for plastically deforming and strengthening the links, which are intercoupled by rocker pins, of a complete endless transmission chain, said apparatus comprises a first and a second pair respectively of conical supporting surfaces for the ends which protrude outside said links of the rocker pins of a transmission chain, mounted thereon, said surfaces having a controllable mutual distance, the invention propose to add a third similar pair of supporting surfaces, provided for cooperation with the first and second shaft. This measure also speeds up the treatment of the transmission chain.