Abstract: Apparatus and process for intermingling a synthetic continuous filament multifilament yarn at substantially any point on a synthetic filament yarn threadline by subjecting the yarn to simultaneous action of two opposed fluid jets which are radial and perpendicular to the yarn threadline. The apparatus has a yarn processing bore which is circular in cross-section and has a length to diameter ratio of from 1 to 2 to 2 to 1. The air entry ports of the apparatus are radial to the bore and opposed to each other in a common plane which is substantially perpendicular to the longitudinal axis of the bore.