and a threading slot 2 opened across the circumference of said ring 3 though the balloon control ring 3 of the present invention looks similar to conventional ones externally its inner circumference has an improved configuration which is described in detail hereafter the improved balloon control ring 3 has a series of annularly elongated aligned grooves 4 separated from each other by respective bank portions 5 formed in the annular or circumferential direction of the ring centrally of the width of the inner circumferential surface of the ring each bank portion 5 being so provided as to divide two adjacent said grooves 4 said grooves 4 and bank portions 5 of the balloon control ring 3 are so formed that the inwardly facing surfaces of the bank portions 5 will not project further towards the center of the balloon ring than the two yarn contacting surfaces 6 6 which project respectively adjacent to and along the upper and lower sides of each of the grooves 4 in operation as the yarn y which extends axially through the ring is turned along the inner circumferential surface of the balloon control ring 3 while being drawn in axial direction the air streams.