Carb Cap Bubble shaped with directional cyclone slits, works great with terp pearls. The air slits send air around the banger in a cyclone manner, moving the pearls at a high rate of speed. Terp pearls will not spin in round bottom style bangers, they need a flat surface to work. Includes two clear pearls. Fits all bangers with a OD of 25mm. The OD of bubble cap is 22mm.