The present invention relates to coupling structures. More particularly, this invention relates to the structural improvement of external and thread coupling parts and to a screw thread coupling structure that can allow the external-threa and internal-thread coupling parts to be rapidly coupled to each other. A screw-thread coupling structure is disclosed. The screw-thread coupling structure includes external and internal-thread coupling parts. The external-thread coupling part forms external-thread formed sides and external-thread not formed sides. The internal-thread coupling part forms internal-thread formed sides and internal-thread not formed sides. The external and internal-thread coupling parts can relatively enter each other, in parallel, and then couple to each other, thereby reducing the coupling period of time.