Abstract: A principal guide-plate (12a) is bent adjacent a first edge (13a) to define a retention groove (9) extending along an axis (y,y'). A secondary guide-plate (12b) is mounted parallel to the principal guide-plate with a first edge (13b) disposed parallel to and spaced from the principal guide plate first edge. A lever (16) is pivotally mounted (21) between the guide plates. The lever defines a cam surface (26) and a locking surface (25) for engaging a safety line (6) disposed in the retention groove. The lever has an aperture (23) at a second end for receiving a safety catch (5). The guide plates define a lower surface (17a, 17b) with a smaller radius (R1) and an upper surface (18a, 18b) with a larger radius (R2). A radial stop surface (20a, 20b) extends between the upper and lower arcuate surfaces to engage the safety-catch and prevent the lever from pivoting from a closed position (FIG. 10) in which the locking surface engages the safety line toward an intermediate position (FIG. 9) and an open position (FIG.