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Four threads, really?

See this spark plug? Notice how the threads are black at the bottom, then turn yellow-ish, and then just clean silver metal-colored.

I've checked: there are only FOUR threads in the cylinder head holding that spark plug. I've thought Ford only made that mistake once, in their old 5.4 V8 two-valve engine - the one that is notorious for spitting out the spark plugs. But no, they made the same thing again, this time in the new 5.0 V8.

Why are they doing that? I don't know, but I can imagine it has something to do with the heat transfer from the plug to the cylinder head metal. Maybe? It is still a wrong decision that doesn't leave much room for errors. Overtorque the plug upon installation, and the four threads get easily stripped. Should carbon happen to deposit on the lower threads exposed inside the combustion chamber, and the plug gets very hard or impossible to remove. Resulting in routine maintenance turning into major engine repair with the bill in thousands of dollars

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