[T3] Battery Cable Bolt/Nut

[Gary Forsmo]

The original, METRIC Square-head bolt and accompanying Hex-head nut on
my battery lugs:  The nut on the ground strap and "hot" cable are
getting "rounded", to the point that they are difficult to make tight.
What metric size bolt (thread and length) and nut do I need for my 1969 Square?

The car is stored 1,500 miles away in Wisconsin while we are in Texas
for the winter.

McMaster-Carr http://www.mcmaster.com/#metric-hex-nuts/=ksiqmr

Gary "Frito" - '69 Variant, FI, MT
Rockport, TX (winter)
Lake Geneva, WI (summer)