Abstract: An air diffuser for under floor air and electrical distribution systems, which can be rapidly converted to a cable grommet assembly, is provided with a diffuser grille having generally helical slots that produce a swirling air flow pattern with low impulse, low turbulence and high induction. The helical air slots allow the grille to be rotated or spun off a mold, which allows the grilles to be molded more rapidly and economically. The grille sets on a housing which contains a flow regulator. Both the housing and the flow regulator have side walls with air slots. The regulator is connected to the grille and can be rotated by rotating the grille to regulate that air flow through the diffuser. The air diffusers and cable grommet assemblies are supported by common mounting systems that can be installed through the floors of overlying an air distribution and electrical cable plenum.