I bought a house that has a copper gas line that used to go to a gas dryer. I no longer have the gas dryer and don't intend to get another. The previous owner didn't cap the line. I was willing to give the excess line to the plumber who came for a different job, if he capped the line (he supposedly had the materials for gas in his truck). He came back with a 4" black iron capped rod. To me, it seemed too heavy for the copper line. So I told him, "No thank you." Was I wrong to send him away? Can you cap a copper gas pipe with a black iron? By the way, I'm in Georgia. It's okay to run gas lines in copper.