The square threaded bolt is used to join two plates together. It the bolt has a mean diameter of $\backslash ($ d $\backslash )\backslash (=20\backslash$mathrm$\{$~mm$\}\backslash )$ and a lead of $\backslash ($ l$=3\backslash$mathrm$\{$~mm$\}\backslash ),$ determine the smallest torque M required to loosen the bolt if the tension in the bolt is $\backslash (\backslash$mathrm$\{$T$\}=40\backslash$mathrm$\{$kN$\}\backslash ).$ The coefficient of static friction $\backslash (\backslash$left$(\backslash$mu$\_\{$s$\}\backslash$right$)\backslash )$ between the threads and the bolt is $0\mathrm{.}15.$

Figure $31.$ Joined plates