A clamp for connecting panels in a surface coating structure to a base frame, the clamp comprising: - a fixable element, that is rectangular prismatic, to be fixed to the base frame, having long sides, a top surface, a central longitudinal axis (x), an upper hole and a lower hole, both communicating and concentric along a second axis (y) perpendicular to the central longitudinal axis (x), and - a rotatable element rotating with respect to the fixable element about the second axis (y), the rotatable element having - an upper part that projects from the fixable element after its rotation, and is provided with ends (21, 22) which are, in use, adapted for engaging lateral grooves of panels that are adjacent, - an intermediate part, which is formed by a first disc and housed in the upper hole of the fixable element, - a lower part, which is formed by a second disc, having a diameter larger than the disc of the intermediate part, and being housed in the lower hole of the fixable element with a clearance fit, in order to enable the rotation of the rotatable element with respect to the fixable element, characterized in that the upper hole of the fixable element is tapered downwardly and the lower hole of the fixable element is cylindrical, and the first disc of the intermediate part of the rotatable element is cylindrical and the second disc of the lower part of the rotatable element is tapered downwardly, the second disc and the upper hole being correspondingly tapered for the forced insertion of one in the other. - a fixable element, that is rectangular prismatic, to be fixed to the base frame, having long sides, a top surface, a central longitudinal axis (x), an upper hole and a lower hole, both communicating and concentric along a second axis (y) perpendicular to the central longitudinal axis (x), and - a rotatable element rotating with respect to the fixable element about the second axis (y), the rotatable element having - an upper part that projects from the fixable element after its rotation, and is provided with ends (21, 22) which are, in use, adapted for engaging lateral grooves of panels that are adjacent, - an intermediate part, which is formed by a first disc and housed in the upper hole of the fixable element, - a lower part, which is formed by a second disc, having a diameter larger than the disc of the intermediate part, and being housed in the lower hole of the fixable element with a clearance fit, in order to enable the rotation of the rotatable element with respect to the fixable element, - an upper part that projects from the fixable element after its rotation, and is provided with ends (21, 22) which are, in use, adapted for engaging lateral grooves of panels that are adjacent, - an intermediate part, which is formed by a first disc and housed in the upper hole of the fixable element, - a lower part, which is formed by a second disc, having a diameter larger than the disc of the intermediate part, and being housed in the lower hole of the fixable element with a clearance fit, in order to enable the rotation of the rotatable element with respect to the fixable element, the upper hole of the fixable element is tapered downwardly and the lower hole of the fixable element is cylindrical, and the first disc of the intermediate part of the rotatable element is cylindrical and the second disc of the lower part of the rotatable element is tapered downwardly, the second disc and the upper hole being correspondingly tapered for the forced insertion of one in the other.