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Re: Structural Nut Grades

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It's not unusual to want a softer nut than bolt.  This reduces galling and allows the nut threads to yield, providing a larger area of contact along the plane of the threads.  One of the key issues is whether the shear area of the nut will develop the tension capacity of the bolt (or the desired tension capacity of the joint, or the preload required to set the fastener if the bolt acts in shear). Remember that you get the major diameter of the nut vs the minor diameter of the bolt.

In addition to the other references, I find Mark's Standard Handbook for Mechanical Engineers a useful reference. It has all of the common sizes and grades tabulated, along with commentary on the uses and pitfalls of some of the fastener types. And that's just in one of the twenty or thirty chapters.


At 03:39 PM 11/15/2004 -0800, you wrote:
My ignorance is showing here.
I have, in the past, assumed that when I specify a bolt, that the associated nut will have the equivalent strength.  Recently I was asked to OK a mix & match scenario.  We are using a 50ksi threaded rod with a washer & nut for anchorage into concrete.  I was asked if a grade 5 nut would suffice.
I would normally take a grade 5 nut to have an equivalent strength for an A307 bolt, and a grade 8 nut for A325 & A490 bolts.
1)    Is this correct?
2)    Can I use a grade 5 (grade B to ASTM A563) as a suitable connection to a 50ksi threaded tension rod?  Should I spec the grade 8.
3)    Where can I reference the mechanical properties for nuts?

Thor A. Tandy P.Eng
Victoria, BC
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