Help request, bolt size, back of LT1 head

[Sean 94z28]

I'm 2 hours and 45 minutes, and 4 Fat Tires into this (head removal), and not having luck finding out the size of the hardware that holds the coolant pipes to the back of the heads near the firewall. I am about to eat dinner and if you could help I'll toast my 5th Tire in your honor.

I didn't find metric wrench that would work, what size is that sucker? 3/4, 7/8?????

Thanks in advance!
SEan

[Sean 94z28]

15mm, socket won't work (no clearance) and I can't get the open end on good enough.

of to Walmart for a cheapy box end so I don't strip that puppy. Second six of Tire too, think I'll make the wife drive though. Can't make it to Sears from here by 9:00.

Sean