Gap Gauge for Denso X27EPR-U Spark Plug

I'm not familiar with this plug's design, but if you mean the spark gap is between two curved surfaces, as in many traditional aviation plugs, you should use a wire feeler gauge not a flat blade feeler gauge. Does that make sense?

That totally makes sense to me.  I've been trying to find a good metric wire feeler gauge, but not having much luck.  I suppose I could use an English one.  The ones I've seen have a value of .632mm and that's between the .6 and .7mm that it's supposed to be for that plug.

The traditional 25 thou'. What could be better?

Like Mike said!
0.6-0.7mm is 0.024 - 0.028" ... 25 thou fills the gap!

The U-Shaped Electrode is a Denso Invention.

- - -

It is interesting to note on the Denso Web Site... " (Denso) spark plugs are not for use in any aircraft engines... ".
Just like the NGK are also not! 

Stay tuned for future announcements!  ?

That's what happens when lawyers get involved....

The box actually has a symbol of an airplane with the classic red circle with the slash across it...

With the shape of that "U-Groove" it seems that a flat gauge is perfectly fine.  "25 Thou" it is! ?