Assuming you are asking about an anti-rotation device on an 8 inch pole for a steel floating roof, in my experience hollow rollers work fine - extra strong pipe or thicker. When sparks are an issue you can put a brass sleeve over the steel pipe. I've never seen or used solid round stock but see no reason why it would not work. There is no standard that I am aware of. Then again, if your situation is unusual and you expect very high forces, wear, corrosion, etc then an engineering evaluation should be done by one familiar with the industry and your conditions.