Whether you’re assembling a flanged pipe, bolting manhole covers or other bolted connections on equipment, or even putting together your own furniture, it’s important to take the time to do the job right. That includes ensuring that all the parts are correctly installed and tightened. Otherwise, your connection could come loose and fall apart under stress.
In many cases, a nut is screwed onto a bolt only partially, which weakens the joint. A nut is designed to hold the forces placed on the flange-bolt combination, so it needs to be completely screwed into place. That’s why it’s important to use a wrench to get the nuts to the right torque.
If you’re using a socket wrench, you can help ensure that the nut is fully screwed into place by checking the width of the flats on the head. A full nut will have a hex width of about 0.445" across the flats. If the hex is too narrow, you should consider using a lock nut, which has a smooth top that sits flush against the bolt when tightened.
Another option is to use a single chamfer nut, which has one side that’s flat and the other side with the points rounded off. This design is more ergonomic than a full nut and makes it easier to place the nut on the bolt, helping to eliminate mistakes and save time.
The smooth, chamfered end of a hex nut also helps to distribute the load. Sharp nicks, such as those on a square nut, concentrate the stress in a small area and can break off the threads. A smooth transition relieves stress and allows the threads to extend further.
When installing a single chamfer nut, it’s important to note that there’s no requirement for the ID markings to be raised. This is because, in most situations, the nut won’t be removed after installation and the ID marks won’t be visible. Besides, raising the markings would make it difficult to inspect the nut for defects.
A hex nut can have either a finished or heavy hex pattern, depending on the application. A finished hex pattern has opposite slots cut into the top of the nut through the centers of the flats, which is used to insert a cotter pin when using the nut with a drilled shank fastener. A heavy hex pattern is made from a higher quality steel than a finish hex nut and can withstand a larger proof load. Both of these types are available in a variety of sizes. They’re often used with flanged pipes or in high-pressure applications. A hex nut can also have a chamfered tip to help prevent cross-threading. A chamfered tip also aligns the nut with the mating threads on the bolt or rod, making it easy to install and remove and reducing the risk of error. A hex nut may also have a threaded point to prevent it from loosening under vibration or high-speed operation.
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