TRUaire's T-Bar Step Down Supply Diffusers go by many names, including cone diffusers, Lay-in diffusers, and T-Bar diffusers. The term "T-Bar" comes from the shapes of the railing that hold the ceiling tiles in a drop ceiling. The railing forms a grid of squares and T-Bar diffusers are designed to fit, or "lay-in" to those grid squares. The "cone" shape of the diffuser allows for maximum volume of airflow into the air-conditioned space. These Step Down Supply Diffusers feature a pristine white powder coat finish, extra heavy gauge steel, Seismic support tabs, and TRUaire's exclusive Super Collar to prevent any flex duct slippage or buckling under the pressure of a zip-screw gun. Options include choice of a two or three cone diffuser, choice of collar size, insulation, and either a SmoothGlide butterfly or radial damper. TRUaire™ Step Down Supply Diffuser, 4-Way, Series: 2004CD, 23-3/4 x 23-3/4 x 4-3/4 in, White, Steel, White Powder Coated