This Black Leaf adapter connects 18.8 bongs with 18.8 bowls. The little holes at the underpart of the adapter, called diffuser, divide the smoke in many small bubbles. Many small bubbles have a bigger surface, so you get a softer and cooler smoke experience.
Tube diameter: approx. 13mm
hole diffuser (holes drilled and melted)
*measured from the cross sections upper edge