Portable Air/Fuel gauge?

Saving money on an O2 bung:

Go to your local "real" nut and bolt store and buy some 18mm nuts, don't remember the thread, but same as Ford 18mm spark plugs. I think I paid less than a buck and a half for nuts

And if you have an old 18mm plug, you can use that for a plug if you want to remove the O2[/QUOTE]

Thanks 67Dart273 for the bung info. I assume I'll save some $$$ taking your suggestion if I'll be adding them to several different vehicles.