A levelling spacer device for the laying of slab-shaped products for coating surfaces, comprising: - at least a base having a lower surface and an opposite upper surface defining a support plane for at least two slab-shaped products placed side by side, wherein the support plane defined by the upper surface is placed at a first distance from the lower surface; - a spacer bridge provided with: ∘ two legs placed side by side with each other along a flanking direction and each one rising from a respective portion of the upper portion of the base in a direction orthogonal to the support plane, wherein each leg is frangibly connected to the respective base portion by a predefined fracture line placed at a second distance from the lower surface greater than the first distance, wherein the fracture line is formed by a longitudinal cut with a longitudinal axis that is parallel to the flanking direction; and ∘ a crosspiece, which joins the top of the two legs along the flanking direction; and - a through opening adapted to be crossed by a pressure wedge along a crossing direction orthogonal to the flanking direction, wherein the through opening is peripherally delimited at the top by the crosspiece of the bridge, laterally by the legs of the bridge and at the bottom by a central portion of the upper surface of the base coplanar with the support plane characterized in that each leg has a respective connecting foot protruding from an inner side of the respective leg projecting into the through opening, wherein each connecting foot has a bottom joined to the upper surface of the base, a proximal lateral end joined to the respective leg, a free distal end separated from the distal end of the other connecting foot and a top wall facing the crosspiece, wherein the top wall of each connecting foot has a maximum distance from the lower surface of the base lower than or equal to the second distance and is tilted at an acute angle to the support plane so as to define a ramp rising from the distal end to the proximal end. - at least a base having a lower surface and an opposite upper surface defining a support plane for at least two slab-shaped products placed side by side, wherein the support plane defined by the upper surface is placed at a first distance from the lower surface; - a spacer bridge provided with: ∘ two legs placed side by side with each other along a flanking direction and each one rising from a respective portion of the upper portion of the base in a direction orthogonal to the support plane, wherein each leg is frangibly connected to the respective base portion by a predefined fracture line placed at a second distance from the lower surface greater than the first distance, wherein the fracture line is formed by a longitudinal cut with a longitudinal axis that is parallel to the flanking direction; and ∘ a crosspiece, which joins the top of the two legs along the flanking direction; and ∘ two legs placed side by side with each other along a flanking direction and each one rising from a respective portion of the upper portion of the base in a direction orthogonal to the support plane, wherein each leg is frangibly connected to the respective base portion by a predefined fracture line placed at a second distance from the lower surface greater than the first distance, wherein the fracture line is formed by a longitudinal cut with a longitudinal axis that is parallel to the flanking direction; and ∘ a crosspiece, which joins the top of the two legs along the flanking direction; and - a through opening adapted to be crossed by a pressure wedge along a crossing direction orthogonal to the flanking direction, wherein the through opening is peripherally delimited at the top by the crosspiece of the bridge, laterally by the legs of the bridge and at the bottom by a central portion of the upper surface of the base coplanar with the support plane