In combination, first and second platens (114, 116) of an injection molding machine, a tie bar extending from the second platen to the first platen, and a locking device (200, 600, 700) for releasably securing together the tie bar and the first platen, the locking device comprising: a) a housing (225, 625, 725) extending along an axis coaxial with the tie bar and including a first bearing surface (222, 622, 722) affixed to the first platen; b) a lock nut (223, 623, 723) received in the housing and rotatable within the housing about the axis between locked and unlocked positions, the lock nut comprising: i) an inner bore (230, 630, 730) with radially inwardly projecting engagement elements (231, 631, 731) that engage the tie bar when in the locked position to transfer an axial clamp load from the tie bar to the lock nut, the radially inwardly projecting engagement elements provided along a first axial extent (251, 651, 751) of the lock nut and defining a tie bar engagement portion (235, 635, 735); ii) an outer surface (232, 632, 732) with at least a first step face (234, 634, 734) for abutting the first bearing surface to transfer the axial clamp load from the lock nut to the first platen, the first step face having a first radially outer extent (277, 677, 777); and iii) the lock nut including a narrowing section (237, 637, 737) having a second axial extent (249, 649, 749) bounded by a first position (241, 641, 741) adjacent a proximate side of the first step face and a second position (243, 643, 743) spaced axially from the first step face in a direction towards the second platen, wherein the outer surface has a first diameter (245, 645, 745) at the first position and a second diameter (247, 647, 747) at the second position, the first diameter being less than the first radially outer extent and greater than the second diameter; and c) a retainer (238, 638, 738) mounted to the first platen for engaging the lock nut and holding the first step face against the first bearing surface whether or not a clamp load is being applied across the platens. a) a housing (225, 625, 725) extending along an axis coaxial with the tie bar and including a first bearing surface (222, 622, 722) affixed to the first platen; b) a lock nut (223, 623, 723) received in the housing and rotatable within the housing about the axis between locked and unlocked positions, the lock nut comprising: i) an inner bore (230, 630, 730) with radially inwardly projecting engagement elements (231, 631, 731) that engage the tie bar when in the locked position to transfer an axial clamp load from the tie bar to the lock nut, the radially inwardly projecting engagement elements provided along a first axial extent (251, 651, 751) of the lock nut and defining a tie bar engagement portion (235, 635, 735); ii) an outer surface (232, 632, 732) with at least a first step face (234, 634, 734) for abutting the first bearing surface to transfer the axial clamp load from the lock nut to the first platen, the first step face having a first radially outer extent (277, 677, 777); and iii) the lock nut including a narrowing section (237, 637, 737) having a second axial extent (249, 649, 749) bounded by a first position (241, 641, 741) adjacent a proximate side of the first step face and a second position (243, 643, 743) spaced axially from the first step face in a direction towards the second platen, wherein the outer surface has a first diameter (245, 645, 745) at the first position and a second diameter (247, 647, 747) at the second position, the first diameter being less than the first radially outer extent and greater than the second diameter; and i) an inner bore (230, 630, 730) with radially inwardly projecting engagement elements (231, 631, 731) that engage the tie bar when in the locked position to transfer an axial clamp load from the tie bar to the lock nut, the radially inwardly projecting engagement elements provided along a first axial extent (251, 651, 751) of the lock nut and defining a tie bar engagement portion (235, 635, 735); ii) an outer surface (232, 632, 732) with at least a first step face (234, 634, 734) for abutting the first bearing surface to transfer the axial clamp load from the lock nut to the first platen, the first step face having a first radially outer extent (277, 677, 777); and iii) the lock nut including a narrowing section (237, 637, 737) having a second axial extent (249, 649, 749) bounded by a first position (241, 641, 741) adjacent a proximate side of the first step face and a second position (243, 643, 743) spaced axially from the first step face in a direction towards the second platen, wherein the outer surface has a first diameter (245, 645, 745) at the first position and a second diameter (247, 647, 747) at the second position, the first diameter being less than the first radially outer extent and greater than the second diameter; and c) a retainer (238, 638, 738) mounted to the first platen for engaging the lock nut and holding the first step face against the first bearing surface whether or not a clamp load is being applied across the platens.