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You might think that a nut is simple to design. These small components are essential and play a major role in the building fasteners industry. Designers work long and hard to avoid the common pitfalls facing the humble nut.
Thread Shear
Threads are just as important on a nut, providing the mating surface required for a secure fit. The height of a nut needs to be sufficient and contain enough thread otherwise thread shear is a likely result. Progressive shear also occurs when the load is not distributed well. This most often occurs when the material used is too stiff and does not offer flexibility and thread engagement.
Improper Thread Angle
The angle of the thread is vital and provides the proper balance for contact stress. Too steep or too flat and the stress will result in shear (vertical stress) or dilation (horizontal stress). An enlarged diameter is the natural result of dilation, which will then defer the joint load to the thread tips, the weakest spot.
Crushed Bearing Surface
If a nut is designed with an insufficient width along the flat surface, the result is often termed crushing. The bearing down surface is inadequate and high levels of unit stress crush that surface. In the end bolt tension will relax, an unwelcome condition is almost any application.
Get the Right Goods
Your trusted fastener distributor will supply hex nuts that meet ANSI standards. These products will also be of sufficient height to stand up to higher thread tensions. Thickness of the wall will handle dilation under loads and the proper size of bearing area will prevent crushing.
Your fastener distributor may also recommend a heavy nut, which is even higher and wider across the flats. Heavy components are often paired with structural bolts or in applications with oversized holes.
Building fasteners come in many different shapes, sizes and materials. Nuts may seem insignificant, but without proper design these small components will fall prey to problems like thread shear, dilation or crushing. And any of those can result in fastener failure. Make sure that each fastener element is strong enough to handle the load and your application is sure to be durable.