Abstract: Apparatus for fastening to adjacent substantially co-axially disposed reinforcing rod ends a sleeve of uniform external cross-section throughout its length and having internal cross-sectional dimensions to enable it to receive and embrace both rod ends, comprising at least two fluid pressure operated jack units each having a cylinder, a piston and a piston rod; latching means for releasably securing the jack cylinders together in parallel spaced relationship to one another around one of the reinforcing rods in a zone not occupied by the sleeve; at least two die segments, which collectively provide an axial bore at least part of which is dimensionally smaller in cross-section than the external cross-sectional dimension of the sleeve, loosely mounted on the free ends of the piston rods so as to be capable of limited rotational movement relative thereto in a longitudinal direction; die segment retaining means at the extremities of the piston rods; ring-shaped locking members for temporarily securing the die segm