Ah, that makes a helluva lot more sense...like the dielectric grease for headlight/tailight bulbs etc. Increase connectivity and supposedly help prevent corrosion.
Although if this works anything like that does I'll save the cash and just stick with cleaning the connectors on a regular basis.
EDIT: I'm still missing why you need to use conductive grease if you're just using it for the cap end threads...but I wasn't an electrical engineer (Obviously)
The body of the tube (including the threads) are the negative side of the electrical circuit.
From the positive end of the battery, the current runs through the circuit board to the center of the 510 connection which goes to one side of your coil. The return path goes from the other side of the coil to the outside (the threads) of the 510, to the tube itself, across the endcap threads, through the endcap into the spring which completes the circuit.
