Features: 1.Installation Location: Butterfly shaped vents are installed in the cabin to ventilate the door, cockpit and cabin, allowing smooth ventilation in the cabin. 2.Mounting Size: These edge fixing holes diameter of butterfly vent is 0.138 inches, applicable for 3 mm bolts or rivets, easy to install, you can install it within sereral minutes. 3.Anti Rust Polishing Surface: Made of 304 stainless steel, the surface of the outlet plate is processed by high precision mirror polishing, which is resistant to marine environment and rustproof. 4.With Center Knob: Manual handle design, by rotating the center knob, you can control the opening and closing of the ventilation damper, easy to use. 5.Wide Application: Circular louvered vent covers are usually used for ship support doors, cockpits, cabin ventilation, or for home sheds or other facilities. Specification: Item Type: Butterfly Vent_x000D_ Material: 304 stainless steel_x000D_ Adjustable tuyere size with center handle knob_x000D_ The edge fixing hole is 3.5 mm /0.138 in diameter and is fit for 3 mm bolts or rivets_x000D_ _x000D_ Fitment:_x000D_ Fit for Marine yacht sea RV