The Rocket works great on metal pipe with an outside diameter up to 30mm. That is the approximate outside diameter of 1" EMT pipe (they call it one inch, but the OD is just under 30mm which is 1.17 inches).
It will also work on metal pipe with a smaller outside diameter. It doesn't have to be exact because the retaining pin tightens down to accommodate different size pipe. Use of a smaller diameter pipe may reduce the maximum load. So I recommend using 1" EMT to get the maximum rated load (45lbs).