spout question

Hi, all. I am trying to install a new bathtub diverter spout onto a galvanized steel pipe. I cleaned the threads on the pipe with a wire brush to get the muck out, but I can't screw on the spout. It won't "catch" or latch on. I recently put ceramic tile on that wall and around the pipes so...

Yesterday I removed a bathtub spout because there was a gap between the spout and the wall and I wanted to clean it up and reapply the silicone chalk. I applied silicone tape to the copper and have not been able to get the spout back on. This spout dates back to 1980 and is the screw on type...