Tensile grades for nuts should match bolt grade.

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In a bolted joint, the strength of the nut and bolt should be matched so the fastener system behaves predictably and the joint stays clamped under load. The bolt carries the primary tensile load, and the nut must be able to resist a similar level of tension to prevent it from yielding or stripping before the bolt does. When the nut’s tensile grade matches the bolt’s grade, the clamp force remains reliable and the fastener components fail in a controlled way, if at all, rather than the nut failing first and loosening the joint. Using a nut with a weaker grade than the bolt risks thread stripping or nut failure, which can reduce clamping and lead to joint loss. A nut with a higher grade is acceptable but unnecessary for most standard assemblies and could complicate replacement compatibility; the crucial point is avoiding a weaker nut than bolt. Therefore, the nut tensile grade should match the bolt grade.