Abstract: A device for fixing an object on a supporting surface and having structure for adjusting the position of the object comprises a lower part for fixing against the support surface, an upper part for mounting on the lower part, and locating structure between the two parts for determining the relative position therebetween in two mutually perpendicular directions in the dividing plane between the parts. The locating structure consists of parallel locating strips placed on either side of a rectangular cavity in the lower part. The position of the upper part relative to the lower part in each direction is adjusted by replacing the two locating strips with two other ones of the same total width but with individual widths differing from those of the strips they replace. The upper part is also fixed by a fastener to the lower part and the supporting surface and has structure for fixing the object.