The invention now resides in the provision of very simple and effective means by which such rotational or angular movement of the wires may be prevented. These means comprise a bearing 8 supported by, and rigidly fixed to, that end of the jacking part 5 which is remote from the end portion arranged to be connected with the anchoring head. Such means further comprises a tubular rod 9 which extends within the jacking part 5 along the longitudinal axis thereof'and is rotatably, but axially immovably mounted in the bearing 8. A freely accessible handle member 10, which in the embodiment shown is constituted by a wheel, but which might be replaced by a handle arm, is rigidly connected to the rod 9 beside the bearing 8. By means of this handle member 10 the rod may be held against rotation while the jack and particularly the jacking member 4, 5, is being connected to the anchoring head. Wing means 11 is rigidly connected, as by welding, to the rod end remote from the bearing 8. Such wing means may in clude two radially opposite Wings and may in fact be replaced by three or more radial or substantially radial wings. It is only important that these wings extend until near the inner surface of the jacking part 5, or parts 4, 5, to slide between pairs of adjacent wire endportions when the jacking parts 4, 5 are passed over them. They will thus securely and positively impede a rotational or angular movement of the circular row of wire end portions if the handle member 10 is held against rotation as the tubular jacking part is being rotated to couple it 3 to the anchoring head, whereby the wires will be maintained in parallel, non-twisted relation.