What is the proof load rating for a large diameter (2-1/2”+) nut?

Nuts that are over 2-1/2” diameter do not require a proof load test because most testing equipment in the industry is not large enough to test them effectively. In these cases, a hardness test is an acceptable alternative, unless a proof load test is specifically required by the buyer. Nuts this large would require in excess of 160,000 pounds-force to test the proof load. Since most testing equipment is incapable of this amount, the specifications A194 and A563 have allowed the hardness test as an acceptable alternative for the proof load test for these large diameters of nuts. Portland Bolt stocks many large diameter nuts in plain or galvanized finish. Contact one of our team members for a quote.

From ASTM A194:

“ The manufacturer shall test the number of nuts specified in following all production heat treatments. Nuts that would require a proof load in excess of 160,000 lb/f or 705 kN shall, unless Supplementary Requirements S1 or S4 are invoked in the purchase order or contract, be proof load tested per Section 8 or cross sectional hardness tested per Annex A3 of Test Methods and Definitions A370. Proof Load test prevail over hardness test in the even a conflict exists relative to minimum strength.”

From ASTM A563:

“6.1.2 Jam nuts, slotted nuts, nuts smaller in width across flats or thickness than standard hex nuts (7.1), and nuts that would require a proof load in excess of 160,000 lb/f may be furnished on the basis of minimum hardness requirements specified for the grade in Table 3, unless proof load testing is specified in the inquiry and purchase order.”



    what is the hardness range for your mandral for proof loading 1 1/8″ nuts and up , am most interested, thanks

    @Lucille- We are not doing any nut proof load testing in house, so we do not have any mandrels for that purpose. That said, we think as long as the mandrel you use is at least as strong as the nut that will be proof loaded, you should be ok.


    If Supplementary Requirements S4 is invoked, can the proof load testing still be done by cross sectional hardness tested per Annex A3 of Test Methods and Definitions A370 for nuts that would require a proof load in excess of 160,000 lb/f ie. 1.5/8″ Heavy Hex Grade 7?

    @Michael- If the supplemental for large proof load testing is invoked, then the nut should be tested full size. As far as we understand, the cross sectional hardness testing is independent of proofload testing.

    ASME SA194, the nuts have size 1-3/8″ with proof load values above 160,000 lbf, Could we have a hardness alternative for the proof load test?

    @Adrian – Yes, hardness testing is permitted as an alternative to proof load testing for nuts requiring proof loads exceeding 160,000lbf.

    ASTM A194 table 3 has sizes 1.3/8″ and 1.1/2″ with proof load values above 160,000 lbf.
    Supplementary requirements, S4 do not show values in table S4.1 for these sizes.
    Can you advise what load we test to?

    @Darren- We can see where that is laid out in a confusing manner. The nuts should be tested to the values listed in table 3. The value is calculated by multiplying the proof stress in psi by the tensile stress area of the nut. Example, for 1-1/2-8 A194 2H nut; 150,000psi x 1.492 sq in = 261,100 lbf.

    @John- The nuts we sell would have a proofload test performed, but the other tests are not normally performed. We could however, perform them upon request.

    In the event that you do require proof load testing of your nuts, TUV has a lab in Aliquippa, PA that has a press that is calibrated up to 1,000,000 pounds. Please contact me if you need any more information.

    @Dieu – we are happy to answer any specific questions you might have regarding nut proof load testing.

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