Can someone explain to me what the differences are in sparkplug wire measurements. I've seen for example 8mm all the way up to 10mm wires. Whats the difference and which is better? Also whats best size/brand for a medium boost application(9-12psi)?

 

its all about conductivity and what there made out of, on a real high horsepower car the bigger the better, im boosting in the range of 9-12 psi and my msd wires are just fine, there 8.5 mm and they give me all the spark i need......