Abstract: A yarn treatment jet is provided having a venturi member with a venturi shaped bore, and an inlet member with a yarn passage therethrough located in the mouth of the bore, in which the inlet member is in contact with the mouth of the bore to locate the inlet member positively relative to the venturi member and is configured to provide a passage for air into the venturi bore between the inlet member and the venturi member. The inlet member may be formed of a core and a needle so that to change the configuration of the air passage only the core need be changed. The air passage is formed by one or more grooves or bores in the inlet member or core.