BanMeGayMod

I used to rekey homes in the foreclosure business. The company would send us the pin positions and we would do them as specified. Most companies I worked for would use the same rekey pins for every home. This way after the initial rekey everyone who needed to get into any of the homes already had a key.

What locks/keys can never have a twin?

The third part answered my question. Looking at it now I understand how it doesn't make sense.

To clarify my question should have been worded as "what are the chances of my key opening someone else's door?"