A foundation, arranged for supporting a post in a substantially upright manner in a using position, wherein the foundation having an elongate extension direction (z) similar with an axial direction of the post in the using position, the foundation comprising: - a circumferential wall extending in the elongate extension direction (z) and comprising an upper end and a lower end opposite the upper end, - an interior space arranged to receive and accommodate an end portion of the post, wherein the interior space is formed by that the circumferential wall encloses the interior space, wherein the circumferential wall has a thickness at the upper end thereby providing an upper circumferential top surface facing in the elongate extension direction (z), wherein the upper circumferential top surface is arranged to limit the movement of the post in a radial direction (r), transverse to the elongate extension direction (z), - centering means arranged at the circumferential wall between the upper end and lower end of the circumferential wall and protruding in the radial direction (r), inwards into the interior space, wherein the centering means are arranged to center an end portion of the post in the interior space, - at least one adjusting means arranged at the circumferential wall between the upper end of the circumferential wall and the centering means, wherein the adjusting means protrudes in the radial direction (r), inwards into the interior space, wherein the adjusting means is arranged to adjust the post accommodated in the interior space relative the circumferential wall in the radial direction (r), by the adjusting means being movable in the radial direction (r), and thereby impacting an outside of the post accommodated in the interior space of the foundation, - at least one flexible tongue, extending at least in the elongate extension direction (z) of the foundation and positioned in position and radially inside of the at least one adjusting means, wherein the at least one flexible tongue is arranged to flex radially inwardly when the corresponding adjusting means is moved radially inwardly so that the adjusting means abuts the at least one flexible tongue, characterized by the foundation being made of metal and the foundation further comprising a cover ring, arranged to rest on the upper circumferential top surface and further arranged to fit around an outside of the post, wherein the cover ring further is slidable on the upper circumferential top surface of the foundation, to follow the motion of the post accommodated in the interior space when adjusted in the radial direction (z) by the adjustment means. - a circumferential wall extending in the elongate extension direction (z) and comprising an upper end and a lower end opposite the upper end, - an interior space arranged to receive and accommodate an end portion of the post, wherein the interior space is formed by that the circumferential wall encloses the interior space, wherein the circumferential wall has a thickness at the upper end thereby providing an upper circumferential top surface facing in the elongate extension direction (z), wherein the upper circumferential top surface is arranged to limit the movement of the post in a radial direction (r), transverse to the elongate extension direction (z), - centering means arranged at the circumferential wall between the upper end and lower end of the circumferential wall and protruding in the radial direction (r), inwards into the interior space, wherein the centering means are arranged to center an end portion of the post in the interior space, - at least one adjusting means arranged at the circumferential wall between the upper end of the circumferential wall and the centering means, wherein the adjusting means protrudes in the radial direction (r), inwards into the interior space, wherein the adjusting means is arranged to adjust the post accommodated in the interior space relative the circumferential wall in the radial direction (r), by the adjusting means being movable in the radial direction (r), and thereby impacting an outside of the post accommodated in the interior space of the foundation, - at least one flexible tongue, extending at least in the elongate extension direction (z) of the foundation and positioned in position and radially inside of the at least one adjusting means, wherein the at least one flexible tongue is arranged to flex radially inwardly when the corresponding adjusting means is moved radially inwardly so that the adjusting means abuts the at least one flexible tongue, characterized by the foundation being made of metal and the foundation further comprising a cover ring, arranged to rest on the upper circumferential top surface and further arranged to fit around an outside of the post, wherein the cover ring further is slidable on the upper circumferential top surface of the foundation, to follow the motion of the post accommodated in the interior space when adjusted in the radial direction (z) by the adjustment means.