What's the smallest hole size you can use to run GM loom through firewall?

[Paul Y]

Following on from my 'where did you mount your ECM' it looks as if I have enough cable length to actually place the ECM inside the truck. Phew!

Question is, what is the smallest hole I can drill in order to pass through the loom to the engine?

I have heard reference to it but, after a quick search, have not found a definitive size.

Anybody care to share what they used?

Thanks,

P.