Hex, Self-Locking, Dome and Wing Nuts

The nut, screwed onto a bolt or rod, locks the connection and transmits the tightening force. It is used in metal structures, anchorages and mechanical assemblies, where the connection must remain fixed. The nut must always be matched with a bolt or rod of the same size and thread pitch.

The nut must have the same diameter and thread pitch as the bolt, and the spanner size must match the size of the nut. The material must be chosen based on the environment, for example galvanised steel for general use and A2 stainless steel for humid environments. A mismatched size damages the thread and reduces the grip.

The self-locking nut with nylon insert is used where there are vibrations, because the insert creates friction on the thread and prevents the nut from loosening. It is useful in machinery, motor mounts and mobile equipment. The nut must still be tightened to the value indicated by the manufacturer, because the insert does not replace correct tightening.

The cap nut has a closed dome end and serves to protect the end of the thread, which stays covered and is not damaged. It is useful where a protruding thread could injure people or be damaged by impacts and dirt. It is used for finishes, pipework and exposed parts, such as in installations and equipment.

The flanged nut has a flange that spreads the load and does not need a washer, while the wing nut is tightened by hand without a spanner. The wing nut is practical for frequent adjustments or where there is no room for a spanner. Both must be chosen based on the tightening force required and the intended use.

The coupling sleeve is a cylindrical element with an internal thread, which joins two threaded rods together, while the nut is used to lock a bolt or rod to a plate. The coupling sleeve lengthens the rod; the nut fixes it. The choice depends on the connection you need to make and on the size of the rods.

Hand tightening does not guarantee the required tightness and can loosen with vibration or load. For important connections the nut must be tightened with a torque wrench to the torque indicated by the manufacturer. The wing nut is designed for hand tightening only where the load is not critical.

A worn nut has a damaged thread, with flattened or stripped crests, and no longer screws on smoothly. If the nylon insert of a self-locking nut is damaged or no longer holds, the nut has lost its function. In both cases it must be replaced, because a worn nut does not lock the connection safely.