This Defender Security doorknob lock-out device is designed to be mounted directly over the doorknob to prevent access to the keyhole only, effectively preventing unauthorized access by key. The durable diecast cylinder is held in place with an O-ring and is removable when the device is unlocked and open. The cylinder cannot be removed when the device is closed and locked. This lock-out device is often used in evictions, rentals, home sales, on job sites, in-home, on in-office storage room knobs and more. It is the ideal solution for keeping others out, even if they have a key to the door. It is a quicker and easier solution over replacing the entire knob and lock system on a door while still getting the protection you need. The maximum outside diameter of a round knob that can be secured with this device is 2-7/16”.