Structure of internal thread portion for preventing looseness and method of producing the same

Abstract

It is an object of the invention to provide a structure of an internal thread portion for preventing looseness which structure allows a reduction in the torque required for the threaded engagement with an external-thread member and prevents a seizure. An exit end portion of a self-locking nut is taperingly contracted over the entire circumference thereof so as to form a contracted internal thread portion having a conical section. In addition, ridges of the contracted internal thread portion are provided with corrugation continuing circumferentially. The diameter of an inscribed circle which links the extremities of projections in the corrugation is smaller than the minor diameter of the external-thread member which is to be engaged threadedly with the internal thread portion. With the external-thread member threadedly engaged with the internal thread portion, a plurality of projections press the root or flanks of the external-thread member and are thereby elastically compressed by the reaction, so as to clamp the external-thread member from outside. In accordance with this arrangement, the tightening torque can be reduced and a seizure is prevented.

Dependencies are inferred from the claim text.