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I have the full repair manual for a 2011 IS-F, I looked at the body and exhaust section. I can vaguely see this but they don't refer to it or mention it.
If it's off the car and you got a work car, take it to the Dealership and ask the parts guy what it is. (I'm sure it has a purpose)
My last discussion with Amayama was not good. I had $500 in parts, but they said they could only ship DHL Express. The shipping was $1600. I said no thanks. I've heard Megazip is still reasonable, but the good news about Amayama is they send you a full quote before they take your money. You can always shop them. I hope they change their shipping policy back to what it used to be.