The device has a chord having two strands including double loops, where the loops are forced to pass in an opening (34) having oblong shape. The loops are retained by a snap hook (22) which blocks descent of a user when the user does not exert force on the hook, where the descent is controlled by a force of the user on the hook. Edges of the opening comprise supporting projections (29, 31) for supporting the hook when the user exerts the force for controlling the decent.
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