Blind base U 71 BSK, blind base, base for supporting IBT boxes and boxes with counter formwork in conjunction with support bars, can be combined using a snap connection, when installing the blind base using nail, magnet or adhesive technology, later plastering of the fastening points is necessary, for Assembly: 1. of the U 71 boxes with counter formwork, at a distance of 71 mm. Can also be combined with composite glasses for extreme stress. 2. the installation box K3 EK and K4 EK with counter formwork with 2 or 4 bases and 3 support bars in the corners, 71 x 71 x 21, height 21 mm for magnet fastening, magnet hole must be plastered later,