Speedometer cable.  New in original package.
Star parts says it fits 84-87 L body (Omni, Charger, etc).  It may fit other years and models, but I can tell you for sure that this is the part that connects to the back of the instrument cluster and passes through the firewall into the engine bay.   If you own a Shelby Charger (or GLHS, or Omni GLH, etc..) if you've ever pulled out your instrument cluster there is a chance your speedo cable's clip is busted off.  It happens folks, our cars are old now.   I haven't seen one of these brand new in the package like this, (other than this one), ever.  One left in stock.   Part number is 5003000AA