Geissele made this rod for shooters to check suppressor alignment. The rod for 5.56mm is 15" long, while 7.62mm rod will be 17" long. Both are $75
From: Geissele:
Now available on our website is our Geissele Suppressor Alignment Rod (SAR). The Geissele Suppressor Alignment Rod (SAR) is a precision gage used to verify the alignment of a suppressor to the bore of a firearm barrel.
From: Geissele