PURPOSE: To eliminate play in a thrust direction and a radial direction securely without the smallest strain by providing an elastic deforming part which deforms elastically in axial directions of a helicoid member.

CONSTITUTION: The elastic deforming thread part 5 which deforms elastically in the axial directions of the helicoid member 1 when engaging the female screw of an outer cylinder is provided as a part of a screw thread 3. The thread part 5 consists of a hollow thread ridge type elastic deforming part 6 which has an angle a little bit larger than the included angle of the screw thread 3 and deforms elastically and a column part 7 which supports the deforming part 6, and the hollow part 8 of the deforming part 6 functions to absorb the deformation of the deforming part 6. The column part 7 is formed integrally with the screw thread 3 of the member 1 and the thread part 5 is therefore connected to the screw thread 3 only through the column part 7.