How to measure head bolt size?

[turbosyncrobus]

Here's a dumb question, where on the bolt is the measurement for the size of the head bolt taken? From a JX turbo block/mech. head I have 11.75mm across the threads, and 10.75 on the shank...Help.

[turbosyncrobus]

Thank You very much.

[clbanman]

For measurement purposes, the threads would be measured across pins on the pitch diameter.  For practical purposes measure across the maximum diameter on the threads and round up as they will virtually always be under the nominal.   The measurement across the unthreaded portion may be the same or less depending on the design.  On stretch bolts it will almost always be less here to control the stretch.