slidably receives a rod 23 therethrough with the rod 23 having an abutment plate 25 fixedly mounted to the rod within the cavity 24 the cavity 24 includes a cavity roof 26 spaced from a cavity floor 27 with a spring member 28 interposed between the abutment plate 25 and the cavity floor 27 in this manner hinged orientation of the cap 16 is availed relative to the door first end wall 14 further a cavity bearing strip 29 positioned within the cylindrical side wall of the cavity 24 is arranged for cooperation with an abutment plate bearing strip 30 the strips 29 and 30 are typically formed of teflon or any suitable sliding bearing substance an internally threaded bore 31 is directed into the first end wall 14 as well as into the second end wall 15 each to receive an externally threaded adjustment rod 32 having an adjustment rod head 33 rotatably mounted within the floor plate 20 and the interior surface 21 in this manner threaded projection of the adjustment rod 32 into the internally threaded bore 31 directs either the first or second end wall cap 16 or 17 into the respective first and second end wall 14 and 15 about an associated bifurcated hinge web 22 fig5 and 6 indicate the lock plate.