1. The problem statement, all variables and given/known data A 400mm hollow shaft is coupled to another 400mm hollow shaft. The pitch circle diameter is 600mm and bolt diameter is 65 mm, and there are 6 bolts. The stress in the bolts is the same as the stress in the shaft. Find the inside diameter of the shaft. 2. Relevant equations Polar second moment (J) = pi/32 (D4-d4), pi r2x6 (for the bolts), pi x R2 - pi x r2 for the shaft, Torque/J= stress/r 3. The attempt at a solution I'm not sure how to equate this without a little more info, ie torque or force. I do not know how to formulate the relationship between the shaft and the coupling without extra data. I've totalled the surface area of the bolts, but I'm not sure how to relate that to the shaft. Can someone send me in the right direction? Was I supplied enough information?