PURPOSE: To provide unlikelihood of loosening and eliminate necessity for use of any washer or the like by forming threads with ones a little larger than standard and ones a little smaller alternately pitch by pitch, and arranging so that two adjoining threads constitute two in the standard pitch.

CONSTITUTION: Two pitches at the tip (on the right) of a bolt 1 are made at the standard pitch, and thereafter it is made with a pitch a little smaller than standard and pitch a little larger alternately pitch by pitch, and therein two adjoining threads constitutes two in the standard pitch. Thereby three types of contacting in standard pitch one another, ordinary, loose, and tight, are generated between the threads of the bolt 1 and nut 2. The tight contacting 5 is produced where the thread width of the bolt is large when nut threads pinching them are distorted so that a restrative force acts. This enlarges the friction force compared with the case with combination of standard bolt and nut, and loosening is precluded without use of any washer etc. To fabricate bolt 1, a computer-controlled lathe is used.