Some strength of materials had been mentioned before, along with various steel specifications. Really, if the bearings are set to the outside, and the forks are as close as they are, I'm thinking if you are jumping the FJR (which we are not) and hitting hard, you'd worry about the shear strength. Other than that, let the bearings do the work and try not to make this into another never ending thread. It's a tube, or is it a rod, or is it a tube......hmmmm?