opposite directions two base members 4 and 20 are formlockingly connected with each other with the web 15 of the base member 4 engaging in the pocket 16 of the base member 20 two attachment members 5 are secured to respective connection walls of the base members 4 and 20 with respective connection means 7 the attachment members 5 are secured to the mounting rails 1 2 with respective rail nuts not shown the bottom 26 27 of the rails 1 2 about each other to insure an appropriate mounting the width t of the connection wall of the base member 5 should be equal to a double height h of the mounting rails 1 and 2 and be twice of the distance a between the parallel walls 13 of the base member 4 20 fig7 shows a plurality of base members 4 secured on a mounting rail 1 the base members 4 are connected to the mounting rail 1 with respective rail nuts 29 one of which is shown before being inserted in the mounting opening of the base member 4 for using the connection element according to the present invention with a passing through rail two attachment members 31 32 are secured to a mounting rail 30 at a distance from each which corresponds to the width of a base member 34 as shown in fig8 a further mounting rail 33 extends through the base member 34 the attachment members 31 32 are secured to the parallel walls of the base member 34 with respective connection means 35 36 fig9 illustrates another possibility of using an attachment member in fig9 an attachment member 37 is secured at the end.