Terp Balls, also known as dab beads or terp pearls, are little glass balls that spin inside a banger to help improve the vaporization of concentrates. To use, pop a terp ball or two into your banger, then heat it up with a torch. Once it cools to the ideal temperature, take your dab as you normally would, using a carb cap with good airflow. The balls will help with heat retention, vaporizing more oil at the same starting temperature.
But to get the max potential out of your balls, you will need to use either a bubble, directional, or spinner carb cap to move the balls around the nail. As they move around, they are not only helping to distribute the heat of the surface they are travelling on, but they move the oil around as well, ensuring that it will hit the hottest spots on the nail and vaporize much, much more thoroughly.
A carb cap does a great job on its own, but combining your banger with a terp ball for a higher level of smoking? THAT is where its at.