The FLATLINE-OPS ADI/ACI Set-Up Tool (TRUE-BORE) makes Angle Indicator Installation a Snap. Attaching Angle Degree Indicators or Cosine Degree Indicators to your firearm is easy, but calibrating them to read correctly isn't so easy. Attach this set-Up tool to the tip of the barrel, and leveling the barrel becomes as easy as centering the bubble between the lines. Speed and ease is what you get with this ultra-lightweight black space-age polymer level. It made from black high strength polymer construction. Instructions included.