Abstract: An apparatus for guiding traveling yarn through a slot in which characteristics of the yarn are sensed, includes a pair of members having surfaces engaging the traveling yarn. The surfaces of the members are spaced from the slot, in respective opposite directions, by an amount sufficient to permit circulation of a fluid therebetween for removing dust and other debris, thereby reducing the distortion of the sensing of the yarn caused by the dust and other debris. The first and second members can be integrally formed from the housing which includes the slot.