The recommended method for physically securing this type of ThinkCentre system is to use a padlock with an optional steel loop cable, as shown in the pictures below.
Cable examples:
Desktop Solution
Padlock loop Your computer is equipped with a padlock loop that locks the cover to your computer when a padlock is installed. Using a padlock at least or at 5mm or 3/16-inch can secure your computer cover to help prevent unauthorized people from gaining access to the inside of your computer.
Tower Solution
Padlock Your computer is equipped with a padlock loop such that the cover cannot be removed when a padlock is installed.