Thread on boot gas strut

[petepetrolhead]

Anyone know what the thread is on the ends of the gas strut that lifts the boot? The threaded insert on the upper part of the hinge has broken off and I need to replace it. I read somewhere on here that the threaded ends were M6 but having bought some M6 inserts they sure as hell don't fit! The outside thread diameter is 7.8mm (yes, I know, should have measured it first - doh!) so I don't think it's M8 (thread looks too coarse) - might be 5/16" but that should be 7.94mm so I'm doubtful.

Any help gratefully received (but I'm not looking for "buy a thread gauge" - though I probably should!!).