Frank, a short flange portion under the head is 11.8 mm thick, then it necks down to 10.75 mm - this portion is 20 mm long. Then the threaded section is 11.8 MM, measured with a caliper - 41 threads at 1.75 mm pitch. The bolt bites about 12 threads into the block.
So, I can assume that the inner thickness of the threaded section is about as thick as the smooth necked-down section above, meaning that both the necked-down section and the first 30 threads above the block are involved in the stretching???, about 70 mm worth.

The entire bolt length under the head is 102 mm, with an allowed reusable length of 105.4!!!!!

Oh, 50 miles of highway today, not a hint of a leak!!!!!!!!

DG