The bubble for shell is acrylic, designed for scoperifle levelingCompact: The for shell is acrylic and, easy to use and compact size for storage Easy to use and compact size for storage and transport Use: Place the Turret on the top cap and the Action the bolt; once the levels show a, and then simply tighten the rings down With strong magnet in the bottom for easy easy use Accuracy: With bubble to crosshairs are aligned for in line placement and doping adjustments, Manufacturer: jklymm