Ford F-150 / 250 / 350 / 450:

1974 Ford F250 lug nuts

I am the proud owner of a 1974 Ford F250.  I purchased the truck about 12 mths ago.  It has about 50,000 miles on it and is in good working order.
The brake light came on the other day, I noticed the master cylinder was low.  I added fluid.  The light came back on and off.

I looked under the truck and the rear driver side drum has fluid on it. 


So I pulled out my 20 ton jack and proceeded to loosten the lug nuts.  First off I couldn't find the lug wrench, there is a small jack that is mounted in the engine compartment, but no lug wrench.


So I pulled out my socket set and it sure feels like 13/16 socket.  SO I went to autozone, picked up universal (one side 13/16) wrench.

Back at home I tried loostening the lug nut, no way - it aint budging.. No sign of rust,, I tried another one - it came loose.. Another one and it seems the wrench is too big?  Is that possible?   The lug nuts all look factory, maybe the wrench is too big?  I couldn't imagine it being metric in 1974.

Regardless my question is what is the correct lug nut and stem size for a 1974 Ford F250.