non-permanent joint
Relating Bolt Torque to Bolt Tension and Preload [see Budynas p. 437-440]:
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thread profile

d_{r}=\sqrt{4A_{r}/\pi}  \Rightarrow  d_{m}=(d+d_{r})/2

\lambda=\tan^{-1}\left(\frac{l}{\pi d_{m}}\right)=\tan^{-1}\left(\frac{1}{\pi d_{m}N}\right)

K = \left(\frac{d_{m}}{2d}\right)\left(\frac{\tan\lambda + f \sec\alpha}{1-f\tan\lambda\sec\alpha}\right)+0.625 f_{c}

T=KF_{i} d

Distribution=\frac{F_{i}}{A_{t}S_{proof}}

According to Budynas, high preload is very desirable in important bolted assemblies being careful not to exceed 90% of the proof strength. Ideally we would measure the final bolt length and use Hooke's Law to confirm that the correct preload has been applied. However, this is not practical in many applications. Therefore, using the Wrench Torque approximation is the next best method.

The following links and guidelines should be helpful:

(1) Most V-thread angles (ISO, NPT, UTS) are 60°, (2) Standard bolt dimensions can be found in table 4, (3) Bolt proof strength can be found in table 5, (4) f and fc are generally close in value (see table 6).
Bolt Nominal Major Dia. (d): Bolt Minor Dia. Area (Ar): Tensile Stress Area (At):
inches inches2 inches2
Thread coef. friction (f): Collar coef. friction (fc): Thread Angle (2α):
Degrees
Threads per Inch (N): thr/in
Min. Proof Strength (Sproof): kpsi
Preload (Fi): lbs [75%-90% of Proof Strength]

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