I'm tapping the front header for a Zeitronics EGT sensor. You can see the front header looking straight down in the front of the engine bay. It's actually very flat and I would consider upside down. Looking up from under the car, you see all the tubes. I need .12 or 3mm thickness to tap for the 1/8 npt27 tap. I would think the headers are at least 1/10th of an inch thick at this location. Does anyone know the thickness of this location or the headers overall.

Here are some pictures of where I'm going to drill.

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