I need to replace the plug wires on my bike.  I read somewhere that the wire size was 8mm.  When I tried the 8mm wires the outer insulation diameter was much larger than the original spark plug wires.  This made it almost impossible to reconnect them to the coil side.  They did fit nicely on the plug cap side. 

Yea im rambling sorry about that.   Bottom line is what size of wire works the best for a replacement???

I believe I have crammed a 8mm in a coil off a vulcan recently, but its carbon core and silicone insulation, bit quite the steel core and rubber insulation you probably are using. But if you want to try 7mm. the 8mm off the other kind squeezes more and you can stuff it in better.
Cool.
Srinath.

Lube it up  a little dielectric grease may help it slip in there