Cage nuts provide a threaded connecting point for a bolt when access to the back of the connection is limited or non-existent. The threaded portion of the cage nut is housed in a square sheet metal frame designed to grab and hold a particular material thickness. When the cage nut is installed in a part, the frame keeps the cage nut stationary while a bolt is threaded into the center hex nut. A nut, bolt and part must be matched to ensure the threaded connection possesses the strength required to adequately hold multiple parts together without it pulling from the base material.
At the top of the nut frames are two opposing tabs that sit at a predetermined distance apart. The gap in the ears determines the thickness of the material that will hold the nut in place without allowing the nut to pull from the base material. A set ear distance does allow for varying material thicknesses as long as the material is thinner than the ear gap. Materials thicker than the ear gap will allow the cage nut frame to gap the material, but the material will not sit in the ears. This causes the frame of the cage nut to pull forward when pressure is applied with a threaded fastener, and the parts secured in the connection will easily pull apart.
Even with the proper material thickness, cage nuts will still pull from the base material if a square hole is too large for the cage nut frame. Cutting the square hole required to install a cage nut requires specific dimensions and must remain perfectly square to keep the nut in place after the connection is made. The tools required to make the square hole include a drill bit matching the size of the cage nut frame and a coarse square or triangle file. Using the tools correctly provides an adequate hole for the installation of the cage nut.
The correct combination of hole size and material thickness ensures the nut frame will hold tight in the connection material. Another factor, bolt size, determines the size of hex nut that resides in the center of the cage nut, and that determines the size of the cage surrounding the center nut. Determining the size of the required bolt is the first step in properly selecting a nut capable of providing enough support for a threaded connection.