Most French pipes are now delivered with an adapter.
This one allows to smoke the pipe with 9mm filter, metal filter or without filter...
If the pipes are delivered with an adapter, you can use it in the following ways:
With a fiter :
With the "zigouigoui" ! (metal filter)
Without "zigouigoui" (metal filter)
Some smokers remove the adapter completely to have a mini calabash system (smoke cooling).