These units are constructed of 18 gauge galvanized steel. The dimensional information below gives overall width and height of the NCS Silencers. All that is required is the intake size and the face appearance of the motor. This would be the D & E dimension as shown in the drawing. In addition to our standard sizes below, this product can be manufactured in many configurations and sizes to custom fit your specific application. A typical pressure drop us 0.75" in the range of 1650 to 18000 CFM.