Cage Nut

A cage nut or caged nut (also called a captive or clip nut) consists of a square nut in a spring steel cage which wraps around the nut. The cage has two wings that when compressed allow the cage to be inserted into the square holes in equipment racks, and when released hold the nut in position behind the hole.

Using cage nuts mounted in square holes provides several benefits over threaded holes directly in the cage. First, one has the flexibility to choose the size of nuts and bolts (like metric vs imperial) at a time after the cage is installed. This also includes mix-and-matching within one cage. Second, they're easily replaceable. Contrast to a pre-threaded cage where if the threads are stripped it becomes more difficult to make use of the hole. Third, this can allow for a better strength-to-weight ratio, as only the nuts need to be made of a strong material suitable for threading.

The nut is usually slightly loose in the cage to allow for minor adjustments in alignment. The gap between the two wings determines thickness of material that will hold nut in correct position without pulling it from the base material. The size of square hole will also govern the position of nut. If size of hole is too large it will still pull out from base material. There are two types of cage nuts:

A) SLIDE-ON:

These nuts are used when rails are square punched because in such a case it becomes easy to move mounting hardware. These nuts are also known as "clip nuts" or "clip on nuts."

B) SNAP-IN:

These nuts are used for rails that are punched with square mountings in data cabinets.

The most common use for cage nuts is to mount equipment in square-holed 19-inch racks (the most common type nowadays). There are four common sizes: 10-32 and to a lesser extent 12-24 are generally used in the United States; elsewhere M5-0.8 (5 mm outside diameter and 0.8 mm pitch) for light and medium equipment and M6-1.0 for heavier equipment such as servers.

Although some modern rack-mount servers have bolt-free fitting, other components such as shelves, networking hardware, UPSs and KVM switches still tend to be fitted using cage nuts.