Two parts of a machine are held together by bolts, each of which carry a static tensile load of 3100 N. 

a. What size of class 5.8 coarse-thread metric bolt is required using a safety factor of 4 (based on proof strength)? 

b. What is the least number of threads that must be engaged for the thread shear strength to be equal to the bolt tensile strength if the nuts are made of steel whose yield and proof strengths are 70 percent those of the bolt steel?

3.1 KN