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.”


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