A fitting, in the form of a mounting collar for installation of a water input nozzle, such as a cleaning head in the floor and walls of a swimming pool, is designed to permit the fitting to be rocked from side to side a limited amount relative to the central axis of a water supply pipe in which the fitting is inserted during initial installation. This is done to allow for installation discrepancies where the water supply pipe is not perpendicular to the surface of the pool where the pipe opens into the pool. By allowing this amount of movement in the installation of the mounting collar, the orientation of a pop-up cleaning head, for example, with respect to the pool floor or wall, is ensured to be perpendicular; so that optimum cleaning of the pool surface during subsequent use of the system occurs.