4" Round Screened Vent - tab style, black - bag of 4 Rain Barrel Vents These round aluminum vents are

These round aluminum vents are easy to install in wood

79  si nfa (square inches of net free ventilation area)

They do not work well in wood

These flush-mount stainless steel butterfly vents open and close with a knob in the center

Vent Cap only

4" Round Screened Vent - tab style, black - bag of 4 Rain Barrel Vents These round aluminum vents are4" Round Black Screened Vent, tab style bag of 4 RBLT 100 4" 4PK These round aluminum vents have louvers and a screen to keep insects out. They are easy to install. They fit into the hole made by a drill type hole saw and are held in place by 4 tabs on the side of the vent. No nails or screws are needed. Note: These are made for thin materials like metal, glass or plastic. They do not work well in wood. The tabs need to be bent over from the rear.