Thread forms for preventing disengagement between male and female screwheads

摘要

The present invention provides a male screwthread that does not loosen. In a male screwthread that has a thread ridge formed on an outer peripheral surface of an axial portion and a head portion that forms a tool mating means at one end of this axial portion, loosening and return between the male screwthread and a female screwthread is prevented (self-locking) by a configuration in which the thread ridge thereof is formed to have a major diameter that is larger than a reference value and the half-angle of the head-portion side of the thread ridge is formed to be less than 30 degrees.