A cage nut is used on a rack that has square mounting holes. You would use a cage nut when you need to mount a product in your rack that requires a threaded hole. A 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 cage nut to be inserted into the square hole and simply clip in. When this is 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. There are 3 common sizes for cage nuts. These sizes are 10-32 12-24 and M6. The size you will require is determined by the product you are mounting. We recommend you purchase the corresponding screw to go with the cage nut. This makes the installation easier if you happen to select the wrong size cage nut.