Curious to know if this has been researched.
This is the type of core plug in the head of my XK120, part number C.2157, also used in Mark VII and XK140.
This is the type of core plug used in a Series 2 E-Type, also listed as part number C.2157 and also used in XJ6.
The thread is the same 7/8-14 UNF for each.
Its kind of odd that they didn’t change the part number, not even a /1 suffix.
My question is this:
When did they change from the internal hex key plug to the external hex head plug?