Ted Edwards wrote:

Grant Erwin wrote:
26tpi gage nor my 27tpi gage appeared to really fit it. It looked to me
like it was in between, call it a "26½tpi" thread. I miked the OD of the
threads and got 0.429" which isn't very close to anything except maybe
11mm.

Likely a 1mm pitch thread since 25.4÷26.5 = 0.958490566

Off hand, I don't recall if 11mm diameter is a stard size but 12mm
certainly is.

Ted

Apparently 11mm is a stardard size in the European automotive
industry as some engines use the size for cylinder head studs.
Albeit of a coarser pitch.

Tom