are octagonal in the exemplary embodiment illustrated openings are formed in the node 1 which are bordered by a triangle the edges of which are formed from the edges 6 of the surfaces 2 in addition the surfaces 2 in the vicinity of their edges 5 also have a groove 9 which is located laterally between two surfaces 2 fig2 shows a profile strip 21 of the prior art with an inserted interlocking element 90 the actuator knob 93 of which projects laterally from a corresponding boring for fastening the profile strip 21 is placed with its one end 22 laterally on a surface 2 of a node 1 so that the clamping hooks 91 and 92 are engaged in a slot 3 or 4 by tightening the actuator knob 93 as explained further with reference to fig8 the clamping hooks 91 and 92 extend behind the slot 3 or 4 and detachably but firmly connect the profile strip 21 with the node 1 instead of an interlock element 90 any other closing or interlock element can also be used in which hooks extend behind a boring or slot on one or both sides the configuration of the profile strip 21 can also be any required shape it is advantageous of course if two grooves 23 for.