Hanger Rod FOS

[FEM4Structures]

1) ASME B31.1 Table 121.7.2(A) – Carrying Capacity of Threaded ASTM A36, A575, and A578 Hot Rolled Carbon Steel
General Notes utilizes a minimum tensile stress of 50 ksi divided by a safety factor of 3.5, reduced by 25%, resulting in an allowable stress of 10.7 ksi.
Question: What does safety factor of 3.5 and further reduction of 25% accounts for? Also, trying to understsand underlying theory behind safety factor of 3.5 and further reduction of 25%. Insights will be appreciated.

Thanks

Thanks,

FEM4Structures