A pin on the flag arm goes into a hole in the door. I welded on a washer for the flag arm pin to go into when the door is closed. I could have bolted on a metal tab with a hole in it. The flag arm is heavier on the end with the flag, so it drops down when the door opens.
The wire on the bottom is to dampen the sound when the arm falls down so it does not startle the mailman. It is easily reset with one hand when I am in my car.
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