The Locking Insert can be purchased with your Keystone mailbox - in which case it is delivered installed.

OR

You can order the Locking insert separately for the Keystone mailbox you already own.  It is delivered to you ready for installation with a single screw, making your Keystone Mailbox a secure locking mailbox.

If ordered separately, the Locking Insert is considered a  NON-REFUNDABLE (except for defects) replacement part.

Locking Insert Dimensions
9 1/8" wide x 5¾ high x 18½" deep.
Incoming mail slot:  7" x 1½"