Size of single huge bolt holding front wheel cylinders to back plates?

[jdarren]

Instead of two bolts, the front brake wheel cylinders are held to the back plates on my '69 C-10 each with a single huge bolt. On the first front wheel I tried, I was able to loosed the bolt with an adjustable wrench. but on the second, it's slipping. I want to buy a socket, if I can find one, but don't know the exact size of the bolt head. Anyone know right off?

[dougf]

Hmm, I ran into the same thing a while ago... I ended up measuring my bolt and bringing it to autozone and buying a cheap socket. let me see if I can find the size.