Abstract: The clamping means of the anti-slip device includes a pair of locking members for selectively clamping the overlapping wire ends of the wire in a manner so as to only permit movement in a sense of a shortening of the effective length of the wire. A pair of release members are actuated simultaneously by a frame so as to move the locking members from an inclined position in which the wires are clamped to an upright position in which the wires are free to move through the locking members. The clamping wire is secured within the helical spring forming the resilient pull element at a point diametrically opposite the clamping means. With the anti-slip device fitted onto a wheel and with the release members in a locking position, the locking members allow the clamping means to move relative to the wire ends only in the sense of a shortening of the effective length of the wire.