I used Iridium's when I raced, and yes, I indexed them. Good plugs.

I forgot to look for them when I put new plugs in the X5. I put in the bmw quad electrode ones replacing single electrode plugs and my mileage has dropped by 1 mpg or so (small sample statistics, I know)...

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Kirk
Las Vegas
2016 X5 40e Mineral White/Black Dakota Leather, ZLL, ZCW, ZDA, ZDB, ZPP, multi contour seats, rear side window shades, HK stereo
2011 E90M3, 6-speed manual