TRIS is the shelf support slotted into the shelf by making edge borings. The sleeve of the shelf support
can be expanded by inserting a pin (pin=optional extra), which improves the structural fastening of the shelf to the sides of the furniture.
The shelf has to be pushed downwards onto the side brackets, which can be screwed into any position required. The side brackets slot into
the socket of the shelf supports and a click locks the shelf in position.