RG2000/413/15OR 2-1/4X12 BROWN FLOOR DIFFUSER | All-steel construction. Widespread air diffusion. Easy to operate damper control. Rolled fin for strength and safety. Measure the length and width of the opening. Subtract 1/8 to 1/4 in (depending on how square the opening is) and this is the inside dimensions. Painted metal registers have a durable powder-coat finish.