Abstract: Provided is a body member having two planar orthogonal yarn-treating faces. Secured to the body member is a cover member having a coacting surface which is either (a) planar or (b) concave, partial conical. The coacting surface of the cover member is spaced from the first of the yarn treating faces to form a yarn passageway. A pair of fluid conduits is provided in the body member, one conduit terminating perpendicularly to each of the yarn treating faces in an orifice therein which is positioned to direct fluid against the surface of the cover member. Fluid is supplied to the conduits from a suitable source, and a mechanism is provided for controlling the velocity and direction of travel of a multifilament yarn into and out of the yarn passageway, most desirably in a traversing movement.