Water meter fitting leaking

I'm afraid I may have messed big time and broken part of my Water meter fittings while making other repairs. There was a three inch nipple of galvanized (I don't know why this was left when the rest of the plumbing was copper) between the main shut off and the meter that was badly corroded. I shut the water off at the curb and replaced it with copper. I replaced the main shut off as well since it appeared to have been repacked recently. Where this attaches to the meter this is a fitting, I'm not sure if it is supposed to be a union, with two hex faces that the nipple threaded into. With the nipple removed the small face turns relatively freely and neither tightens nor loosens. It now leaks between these two faces. I didn't try to turn this when I removed the nipple, Water meter covers but given that it was a bear to remove, I'm not surprised that I did accidently.

Is there something simple I'm suppose to do to tighten this fitting, or did I kill it? If so, can I get a replacement at a plumbing supply house (and if so what do I ask for)?

(I had better luck getting a pic of the top of the fitting than the bottom. They look equivalent.)