PURPOSE: A thermoplastic resin is conjugate spun by the use of a specific spinneret, cooled, drawn and heat set to produce fibers inexpensively, which are suitably used as guts for rackets because of their high water resistance.

CONSTITUTION: A thermoplastic resin, preferably fluorine resin, polyamide, or polyester, is melt spun by the use of a spinneret, e.g., composed of an inner spinneret 2a and an outer spinneret 2b that have been fitted rotation freely wherein each of them are made to rotate with gears 13, 14 and chains 15, 16 respectively. Then, the outside filaments crossed into a network pattern and the inner twisted filaments are fused right beneath the spinneret before solidification, then solidified by cooling, drawn and heat treated.