Oil filter head - different types?

[ChrisDixon]

One for the more detailed/hands on type .... I'm led to believe that the anchor insert that holds the clamping plate to the filter head should have a thread diameter of 3/4 inches or thereabouts. The one on my 3.8S measures 1 inch approx, so I suspect it is off a different era car, a 420 or XJ6 perhaps?

The reason I ask is that on removing an oil cooler adaptor from the filter head I found it was missing the clamping plate, and so far have only managed to obtain a used 3/4 inch one.

All insight appreciated!