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An insert nut is a device hammered or screwed into wood or particle board. Once placed into the wood, the insert nut provides a strong and safe mounting point in which to hang art, pictures or a wide variety of other objects that can be held up by a small bolt. Some insert nuts are constructed of steel or plastic, while others are made of brass. The screw-in type of insert nut is manufactured with threads on the exterior and is threaded into a pre-drilled hole by placing a hex head wrench into the insert and turning it into the wood until tight. The hammer-in version, also known as a knock-in nut, is made with a steel body, occasionally surrounded by a washer-type flange, complete with tiny barbs all around which grab the wood as they are pounded in.
One advantage that the insert nut has over the barrel nut is the convenience of being installed from one side of the wood. Many fasteners require that they be pushed through the wood from the reverse side. This mandates larger holes be cut into the wood or structure to allow access to the reverse side as well as increased time and expense on repairing the access hole. When purchasing an insert nut, it is critical that the proper-size nut be used in the correct size hole. Forcing an insert nut into a hole that is too small can damage the nut; conversely, placing a nut into an over-sized hole will typically result in failure and the nut pulling out.
When drilling the mounting hole for the insert nut, it is mandatory that the hole be drilled deep enough to accommodate the length of the bolt that will be threaded through the nut. Failure to complete this task can cause the insert nut to be forced out of the hole by the bolt as it is tightened against the bottom of the hole. It is also important to place the insert nut flush with the outside edge of the mounting hole. This ensures that the proper amount of insert barbs or threads are gripping the wood. Completing this step will provide the most secure and strongest mounting point possible with this type of fastener.
The size of these fasteners is reflective of the size bolt that is threaded into the nut. The size of the hole required to place the nut into the wood has nothing to do with the indicated nut size. Many nuts are packaged with not only the nut and bolt fastener, but also the proper drill bit required to install the nut into the wood.