grooves 13 thus the slide 20 positively fixes the wire 30 to the post the tensile forces acting on the wire 30 are absorbed via the guide web 11 or 12 respectively and the guide member 21 of the slide 20 the guide member 21 of the slide 20 may be manufactured in sufficient length to afford a specially great contact surface at the guide web 11 or 12 respectively without any difficulty any loosening of the slide 20 from the locked position is made more difficult by providing the wing like side edges 27 with notches extending in part over the lateral surfaces of the t arms 14 or 16 of the guide web 11 or 12 respectively these notches may be pushed and shaped onto the t arms 14 16 upon pushing the slide 20 over the introduced wire 30 they may if necessary be lifted over the wire 30 and subsequently snapped back into positive below the wire 30 when adjustment for example to the wire itself is made in this manner also any unintentional lifting of the slide 20 as well as longitudinal movement is eliminated and the slide 20 can only be moved from its closing position by positive application of force the latter will have to be done only when the connection between pipe 10 and wire 30 is to be separated any breakage of the guide web 11 and 13 in the area of the receptacle.