An assembly technique and device for enclosing an open end of a movable socket (10) comprised of fully hardened materials with an expanding cover-plate (66) and for controlling the expansion of the cover-plate (66) to provide a central orifice (67) of predetermined dimensions to facilitate the installation of a grease fitting. During assembly, various internal components of the movable socket, including the pressure plate, are installed within a housing (12) through a posterior opening (16) with the cover-plate is positioned over the components. A two-stage ram (100) having a contact surface and a concentric pivot punch (142, 158) is brought into engagement with the cover-plate. Pressure exerted by the two-stage ram is transferred to the cover-plate through the contact surface, expanding the cover-plate to conform to the contact surface and enclosing the internal components within the socket housing. The exerted pressure additionally results in the extension of the concentric pivot punch into the central orifice of the cover-plate, controlling the expansion of the cover-plate and establishing the central orifice to predetermined dimensions upon closure of the socket housing.