Abstract: A weft guide channel (6) in a reed of an air jet loom can be lengthened or shortened by telescoping sections forming one or two channel extension members (10, 18) and/or by intermediate inserts (21, 22, 23) that also have a weft guide channel portion (21A, 22A, 23A). The extension member (10) and the inserts are mounted to a mounting bracket (9) which itself is secured to the reed and/or the sley carrying the reed. At least one weft stop motion device is provided for each extension member and/or for the respective insert. One of the extension members is provided with air ducts (14, 15) for a crosswise air flow for stretching a weft thread.