Quote Originally Posted by 914central911 View Post
DIN states that low head conforms with a 4mm internal wrench. Standard height head conforms to a 5mm internal wrench.
DIN specs change over the years. It's been around since 1917. Some DIN-spec M8 nuts from the 356 days are 14mm across the flats. But today DIN would tell you that is 13mm.

In any event the internal hex wrenching feature is 5mm. And the finish isn't black zinc, it's silver.