What's the EASIEST way to plug my 110v gas range into existing 220v NEMA 10-50 outlet. Much appreciated, Jeff
There is no way to do this with adapters.
I take it there's no ground wire in your receptacle junction box.
Neutrals are white or gray. Grounds are green or bare. Any other color is a "hot" and there's no standard. Your two "hots" might both be black, might both be red, might be red and black, who knows.
In every case you'll tear out the NEMA 10-50 receptacle and throw it in the trash. That is a dangerous and obsolete outlet, you'll never use it again.
In every case you'll need to change the 40A or 50A breaker in the service panel to a 15A or 20A breaker. If you know what you're doing, you can make it a single-pole breaker and cap off the unused "hot" and install a cover or spare breaker in the now-empty hole.
You may run into wires that won't fit on outlet terminals. In that case, get a short length of the smaller wire, wire-nut the fat wire to one end, and put the other end into the screw terminal of the outlet. Done.
Option 1: Replace with GFCI
Get a GFCI outlet. Make all your connections to the "LINE" side.
Hot (brass terminal) goes to one of the "hot" wires. Neutral (silver terminal) goes to neutral obviously. Button it up; done. Put the "No Equipment Ground" sticker on the GFCI outlet.
This provides no grounding whatsoever to the stove, but gives protection by sensing current leakage. If you get shocked, it'll turn the power off very quickly.
Option 2: Normal outlet, steal a ground.
Illegal until your town adopts NEC 2014.
Hot (brass terminal) goes to one of the "hot" wires. Neutral (silver terminal) goes to neutral obviously. Bring a ground wire over from wherever you can using any route that works and is legal. The ground wire can go to any other grounded circuit whose breaker is in the same panel. It doesn't need to follow the same route as the original wires, but it'll help the next guy understand if you do.
This answer also applies if, by luck, there's already a ground wire or solid metal conduit back to the panel. You get the ground right there.
Option 3: Re-task wires (illegal)
Illegal because it's illegal to re-mark a "hot" wire to be a neutral or a neutral to be a ground. It's not dangerous to users (if wired right) but it could create a problem if another person later works on the wiring and makes a misconnection because he didn't understand what was done. NFPA's logic is "thinner wires are cheap, just use the right colors, darn it."
You must tear out the 2-pole breaker and replace it with a 1-pole breaker. Mark one of the "hot" wires with white tape - this is now neutral. Tear all the insulation off the neutral wire - this is now ground. Move the new-ground wire to the ground bus (may be the same) and the new-neutral wire to the neutral bus.
Now, up at the receptacle, figure out which "hot" is still hot and which was re-tasked to neutral. There should be 0 ohms between neutral and ground, and infinity between hot and the neutral/ground if the breaker is off. Mark the wires up there the same way.
Now install a 120V receptacle in the conventional way.
This solution is illegal since you're not allowed to re-mark colored wires as neutral, nor white wires as ground.
Option 4: do something lame with ground - illegal, dangerous and stupid.
I'm not even going to discuss this.