How Do Mailbox Locks Work?

Written by ryn gargulinski
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How Do Mailbox Locks Work?
(Photo of crafty mailbox by Ryn Gargulinski)

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Cylinder lock

Mailboxes are secured shut with a type of cylinder lock. The basic set-up includes a key that is inserted into the cylinder, allowing it to move in a clockwise direction. A metal tab is usually attached to the inside end of the cylinder, which moves when the cylinder is turned. The tab begins in a position that stops the mailbox door from opening and, when turned with the key, moves into a position, usually 90 or 180 degrees from where it started, which allows the mailbox door to swing open.


Different tabs may be fitted on the inside end of the cylinder, but the basic set-up remains the same. Some tabs may be slightly raised, bent or hooked on the end to fit snugly into a small opening around the perimeter of the mailbox's door. Others will be flat, with the size corresponding to the size of the latch opening. Instead of a key, the cylinder can also be turned with a thumb latch or a round knob, both of which will keep the door shut but can be opened by anyone, regardless if they have a key or not.


In order to install a mailbox lock, there must be a hole big enough for the cylinder to fit through the front door of the mailbox. The standard size mounting hole for the mailbox cylinder lock is 3/4-inch high and 5/8-inch wide. These holes must be drilled through the mailbox door so the cylinder can be inserted. If the mailbox is aluminium or fairly thin, a bracket can be screwed into place around the front keyhole, securing the cylinder in place.

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