Without Carb Hole
3-part bongs consist of a pipe body, a down-tube and a bowl. The obvious advantage of the 3-part design is that the carb-hole is no longer necessary. On the one hand, this ensures a more aesthetic smoke, on the other hand, you can clean the pipe more effectively as you can seal the joint on the pipe body with a cleaning stopper. This is the only way to avoid using a brush when cleaning, which is the prerequisite for keeping the glass surface unharmed. Having no carb-hole also prevents the spilling of cooling water when slanting the pipe. This is why a lot of people and especially Americans smokers, prefer 3-part models without carb-hole.
Bongs without carb hole