Evidently that’s the standard temperature sensor thread, although there is some dispute (see link below). Mine (Mark X manifold) is poorly fit with sealer by the PO, so I’ve never removed it. Seems like it should have a washer if the thread is straight, but who knows? Jaguar did use UNF threads for similar purposes–the plugs in the oil galleries are 1/2 -20, not BSP.
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