The metal rod is just plain round 8mm rod, preferably in a decent grade of steel. The studding has M8 threads on it. Imperial designs exist if you have or can obtain imperial parts more easily. We don't use ballscrews or any other type of proper leadscrew, since they have cost and availability issues, particularly outside the US. The leadscrews on Z-axis use the same M8 studding as the frame does. Its not an ideal solution but it works well enough for now.
