A 1-8 UNC low carbon steel bolt (diameter = 1.0 in, 8 threads/in) is currently planned for a certain application. It is to be preloaded to 75% of its proof strength, which is 33,000 lb/in2 (Table 32.2). However, this bolt is too large for the size of the components involved, and a higher strength but smaller bolt would be preferable. Determine
(a) the smallest nominal size of an alloy steel bolt (proof strength = 120,000 lb/in2 ) that could be used to achieve the same preload from the following standard UNC sizes used by the company: 1/4-20, 5/16-18, 3/8-16, 1/2-13, 5/8-11, or 3/4-10; and
(b) compare the torque required to obtain the preload for the original 1-in bolt and the alloy steel bolt selected in part (a) if the torque coefficient in both cases = 0.20.
