Crouse-Hinds Extension ring is perfect for use with 4-Inch rectangular steel utility box. This 1-1/2-Inch deep extension ring features steel construction. It measures 4-Inch x 2-1/8-Inch x 1-1/2-Inch. Rectangle extension ring with eight 1/2-Inch side knockouts, hold and protect outlets, switch boxes and small junction boxes. It is perfect for surface mounting and new electrical applications. It has capacity of 10.3-Cubic-Inch. Extension ring is UL listed.