5-64. The device serves as a compact torsion spring. It is made of A-36 steel and consists of a solid inner shaft CB which is surrounded by and attached to a tube AB using a rigid ring at B. The ring at A can also be assumed rigid and is fixed from rotating. If the allowable shear stress for the material is Tallow =12 ksi and the angle of twist at C is limited to 30, determine the maximum torque T that can be applied at the end C.