O2 sensor

Ok I got a DC sports 4-2-1 header used from a friend... went to NAPA and found some flanges for the downpipe off a civic exhaust that would fit... now I am wondering about the extension I need for the O2 sensor... What guage wire is used in the stock setup??? I need to know what guage, and what type of wire (twisted copper?) so that I can make the extension, and not change the resistance of the O2 sensor, which will screw with my gas mileage, and performance of the the engine. I won't be doing this for a couple of days, but please point me in the right direction for the O2 sensor. I am perfectly capable of soldering and extension on, and heatshrinking it. I can get the extension DC sports send with the boxed unit, but it's going to cost me an extra few $$, and I'd like to get this thing on my car in a few days. thanks.

Dude..try not to screw around with the O2 Sensor....it's a bitch