The straight adapter from ‘Black Leaf’ is made of sturdy borosilicate glass with grind SG 19 (18,8mm) on both sides (one side as male, the other as female grind). This means the adapter fits on glass bongs with SG 19.
The following combinations are possible:
SG 19/19 (18,8mm/18,8mm male) or SG 19F/19F (18,8mm/18,8mm female).
The adapter works well as an intermediate smoke filter. You have to use a suitable screen (bowl screen or glass frit with 15mm diameter) and then fill in activated carbon. After that, you stick the bowl into the adapter.
The activated carbon reliably absorbs unwanted substances which arise during combustion like e. g. tar. The taste is smoother, lungs get spared and the bong stays clean longer.