I'm I'm OK at electrical theory but mechanical just doesn't compute. I have the following question if anyone can help. Determine the external diameter of a tube needed to transmit a torque of 30KNm if it has an external diameter twice that of its internal diameter. The sheer stress is not to exceed 80 MPa. Any help would again be gratefully received. Also could anyone tell me how to put formula into this thread as i don't really know how.