$10-11.$ A tool used for compressing a coil spring to allow its installation in a car is shown in Figure P$10-11.$ A force of $1200$ N is applied near the ends of the extended lugs, as shown. Compute the maximum tensile stress in the threaded rod. Assume a stress concentration factor of $3\mathrm{.}0$ at the thread root for both tensile and bending stresses. Then, using a design factor of $2$ based on yield strength, specify a suitable material for the rod.