A hex flange nut with serration is a nut that is formed with an enlarged circular base that flairs out from the bottom of the nut. When the nut is torqued into place, the bearing surface of the serrated base displaces the material of the mating surface. This forms a locking effect which resists vibrational loosening.
Because of the seated surface, the nut will require a greater amount of torque to loosen adding to the locking feature. The flanged surface will span an oversized or a poorly aligned hole and provides a more uniform bearing stress to clamp force ratio than a finished hex nut.
Serrated hex flange nuts are available in Grade 5 and Grade 8.
When using serrated hex flange nuts, the bearing surface will be damaged as the serrations dig, which can cause concerns for engineers. A painted surface will become chipped exposing the material. This may cause accelerated corrosion of the assembled parts.
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