Set Default to specify whether a menu item is the default item in a submenu. Default menu items are executed when the parent item is double-clicked, allowing users to avoid navigating the submenus that contain them.  

The default item appears in boldface. A submenu can have only one default item. If the Items list of the parent menu item already contains a default menu item, setting the Default property to true sets the Default property of the previous default item to false. 

Click 

Parent