What is this extra tab for?

[Boz]

I just got back from purchasing all the needed parts to implement Oscars volume pot. Even though the volume pot from Radio Shack is the same part number, it seems to me there's an extra tab on it and I'm not sure what to do with it. What the hell do I do with this extra tab? Is it a ground or an extra ground?

[BobA]

Looks a bit like a volume pot with a switch built in.   You should check the extra tabs with a VOM and see if they are switched.
Does it click at the far end of its rotation?

[Boz]

No click at either end. Maybe it's an external ground so that I can ground each channel to the chassis this is going in. I have no idea.

[BobA]

It could be a ground point for the sheilds but cannot tell what it is actually connected to from your picture.  You should put a meter on it to determine what exactly it does.   

[Boz]

It could be a ground point for the sheilds but cannot tell what it is actually connected to from your picture.  You should put a meter on it to determine what exactly it does.   

I haven't started connecting wires yet, though I'll be following Oscar's instructions for the volume pot. It's funny. I have a MM but am ignorant for using it. Should I test resistance? (Ohms)

Oscar's Volume Circuit
http://www.oscarcontrols.com/volume/

[BobA]

Oscar's pot looks like the same control with the unused tab.  If you follow his wiring you will be fine.

Just FYI  Use the ohm setting to measure the ohms of the pot or continuity of the circuit.    The most common arrangement of leads is a  common jack and a jack for measurement of AC/DC voltage and a jack for Ohms/Continuity/Milliamps.  To measure ohms your leads should be plugged into the Ohm jack and the Common jack and the mter set at the proper Ohm range or autorange if you have it. 

[Boz]

Oscar's pot looks like the same control with the unused tab.  If you follow his wiring you will be fine.

Just FYI  Use the ohm setting to measure the ohms of the pot or continuity of the circuit.    The most common arrangement of leads is a  common jack and a jack for measurement of AC/DC voltage and a jack for Ohms/Continuity/Milliamps.  To measure ohms your leads should be plugged into the Ohm jack and the Common jack and the mter set at the proper Ohm range or autorange if you have it. 

This is good info. Incidentally, I just gave it a shot and spent the last couple hours stripping, soldering, crimping, etc and I nailed it on the VERY first try. I completely skipped the use of that tab in the back of the vol. pot. and apparently I didn't need it anyway. Volume works wonderfully. Of course the speakers I chose to use for my cab make this thing sound freaking amazing. I'm so glad I decided to face the base drivers down toward the bottom of the cab.

At any rate, I appreciate the input, and in particular the help with the MM. Oscar's instructions worked a charm.