18" x 4" Eyebrow Vent is made of 26 Gauge Galvanized or Painted Steel, Low-Profile, Shingleor Shake Base. This 18" x 4" Eyebrow Vent is a low profile roof dormer vent, with approximate NFA of 40 sq. in. For architectural, residential, and commercial roofing. ASTM A-653, ASTM A-792