Perko Chrome Clam Shell VentilatorPerko clam shell ventilators are ideal for many applications, from covering vent holes for battery boxes, water tanks, and fuel tanks to venting engine compartments. Made of chrome plated brass. Each is pre-drilled for installation (screws not included).Specifications:0315DP1STS Base Dimensions: 1-5/8" x 1-1/2"; Opening Height: 7/16"; Opening Width: 7/8"; Screw size: #4;