What is the standard thread series for A193 bolts?

Unlike most other ASTM specifications covering construction fasteners, the A193 specification requires 8 threads per inch for bolts larger than 1” diameter. The 8 Unified National thread series (8UN) provides increased tensile and shear strength due to a larger tensile stress area and minor diameter and 8 pitch threads reduce the probability of nuts backing off due to vibration.

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