A sanitary fitting comprising a fastening device for fastening the sanitary fitting to a mounting through-hole of a sanitary installation, the fastening device comprising a) a fastening rod connected to the sanitary fitting, the fastening rod comprising at least partially a male screw thread defining a main screw axis, b) a retaining element to be arranged on a side of the through-hole of the sanitary installation opposite to the sanitary fitting, the retaining element having a top end face, a bottom end face, and a hole extending from the top end face to the bottom end face and through which the fastening rod may be passed, c) a securing nut being adapted to be screwed onto the male screw thread of the fastening rod, the securing nut (10, 100) having a bottom end face, a top end face, and a hole extending from the bottom end face to the top end face, wherein d) the hole comprises a screw thread passage and a sliding passage, wherein e) the screw thread passage has an inner surface with a screw thread portion having at least a partial female screw thread and is adapted to engage with the male screw thread of the fastening rod, and f) the sliding passage is adapted to receive the fastening rod and is adapted to allow a sliding movement of the fastening rod without the male screw thread of the fastening rod engaging the female screw thread of the securing nut, wherein g) the screw thread passage and the sliding passage are connected such that the securing nut and the fastening rod may be displaced relative to each other perpendicularly to the main screw axis of the fastening rod between a securing position in the screw thread passage and a sliding position in the sliding passage, wherein h) the top end face of the securing nut and/or the bottom end face of the retaining element comprises a centering surface (34, 48) for aligning the screw thread passage with the fastening rod, wherein i) the centering surface comprises a frustoconically shaped surface portion (34, 48). a) a fastening rod connected to the sanitary fitting, the fastening rod comprising at least partially a male screw thread defining a main screw axis, b) a retaining element to be arranged on a side of the through-hole of the sanitary installation opposite to the sanitary fitting, the retaining element having a top end face, a bottom end face, and a hole extending from the top end face to the bottom end face and through which the fastening rod may be passed, c) a securing nut being adapted to be screwed onto the male screw thread of the fastening rod, the securing nut (10, 100) having a bottom end face, a top end face, and a hole extending from the bottom end face to the top end face, wherein d) the hole comprises a screw thread passage and a sliding passage, wherein e) the screw thread passage has an inner surface with a screw thread portion having at least a partial female screw thread and is adapted to engage with the male screw thread of the fastening rod, and f) the sliding passage is adapted to receive the fastening rod and is adapted to allow a sliding movement of the fastening rod without the male screw thread of the fastening rod engaging the female screw thread of the securing nut, wherein g) the screw thread passage and the sliding passage are connected such that the securing nut and the fastening rod may be displaced relative to each other perpendicularly to the main screw axis of the fastening rod between a securing position in the screw thread passage and a sliding position in the sliding passage, wherein h) the top end face of the securing nut and/or the bottom end face of the retaining element comprises a centering surface (34, 48) for aligning the screw thread passage with the fastening rod, wherein i) the centering surface comprises a frustoconically shaped surface portion (34, 48).