The shelf is secured vertically with wooden dowels between the elements. Horizontally, wooden dowels and iron fittings are used to connect the talars to the side walls. Dowels and fittings are supplied.
So there are no extra screws, brackets or similar to buy as standard accessories, but Tojo seem to consider their construction sufficiently stable with up to 5 elements, i.e. 190 cm high, as can be seen from the examples on Tojo.de.
(I am only a customer and have no other relationship with Tojo or Galaxus).