Is it okay to use a mild steel nut with a high tensile bolt?

Last Updated on July 1, 2020 by Marsh Fasteners

With the latest fasteners on the market, it’s common to see nut thickness standards based on the bolts that they support. This is done because bolts are designed to manage a tensile fracture before the nut strips. The question of whether it’s okay to use a milt steel nut with a high tensile bolt is answered by the performance. For instance, using mismatched grades of nut and bolt can lead to bolts breaking on tightening and gradual thread stripping. To avoid this, make sure that you match your nut grade with that of your bolt grade.

In most instances, standard strength grade bolts and nuts are used in applications. This grade can be verified on the head of the bolt with an 8.8 marking. Now, for the best results and to avoid breaking and stripping, it is best to match this with a nut that has the same strength grade, and in this instance, that is a grade 8 nut.

High tensile bolts are usually graded 10.9 and 12.9 (these are popular varieties) and you can match a grade 10 nut and grade 12 nut with these units respectively. You can, however, replace lower grade nuts with higher grade ones without fear of breakage and thread stripping.


What’s the answer?

No, you should not use a mild steel tensile nut with a high tensile bolt. Match the bolt and nut grade or opt for a nut of a higher grade than the bolt.

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