A nut is a small piece of metal hardware, often hexagonal in shape, with a threaded hole in the center. A packing nut is a nut that is threaded onto a plumbing shaft. Its purpose is to hold packing in place, thereby creating a tight seal in the plumbing. Faucet leaks are often caused by loose packing nuts.
A packing nut is used in many types of plumbing assembly, including valve assemblies, faucet assemblies and commode drainage assemblies. In each case, the nut's job is to create a waterproof seal by creating constant pressure on packing material. The packing material, which can consist of several stacked rubber o-rings or of plumber's tape or string, may be visible or may be contained in a metal or plastic packing box.
Faucet and other plumbing assembly leaks are a common household occurrence. Faucet leaks happen while the faucet is running, and water drips or oozes from areas that are not supposed to weep. The problem may be a loose packing nut, and the solution may be as simple as tightening it.
The first step is to locate the packing assembly, which can be done by consulting the owner's manual or searching online for a diagram of the particular assembly that is leaking. The next is to locate a wrench with the appropriately-sized head that will fit in the available space. Packing nuts can be located in small or hard-to-reach areas, so a short or flexible tool may be required. The nut can be tightened simply by turning it to the right until it again rests snugly against the packing.
It is important to stop turning the nut when it becomes resistant to turning. While it may be possible to force it to turn further, and may seem as if this will create an even tighter seal, an over-tightened packing nut can result in damage to the packing and further leaking. Experts often recommend turning off the water at the shut-off point before beginning any repairs.
In some places, the hardware piece is referred to as a stuffing nut. In any case, the name comes purely from the nut's function. Physically, it does not differ in any way from a standard nut. If a packing nut becomes damaged, a replacement can be purchased at most local hardware or home improvement stores. It is best to take the old nut to the store so a replacement nut of the same size and containing the same thread pattern can be selected.