a base member;

a catch for receiving a wire;

a movable member mounted on said base member, wherein said catch has a first surface extending transverse to said base member and a second surface extending at an angle from said first surface and toward said movable member, wherein said first and second surfaces define a space for receiving the wire, wherein said movable member is mounted for sliding movement relative to said catch from a first position, in which said movable member is spaced from said catch, such that the wire is able to be inserted sideways into the space defined by said first and second surfaces, to a second position, in which said movable member engages the wire and prevents the wire from being removed sideways from said space, wherein said movable member has a surface facing the space defined by said first and second surfaces, said surface facing the space being able to enter said space, at least when no wire is in the space, and wherein said second surface is spaced from said base member, and said space is between said second surface and said base member; and

an urging structure resiliently urging said movable member from said first position to said second position.