This captive cage nut is nothing more than a square nut that has threaded holes wrapped in a piece of spring steel designed like a cage. This spring steel has two flanges that when pressed together allow the nut to be inserted into the square hole and simply clip in. When this done you now have a square hole that is threaded. The nut is typically loose in the cage to allow for adjustments when installing the screw.
Note these nuts will tear up your fingers trying to install or uninstall them with your bare hands. Consider using a Tool.
We stock M6X20MM bolt to go with these M6 captive nuts for your convenience.