Evaluation of anti-loosening nuts for screw fasteners

There are various types of screw fasteners and/or parts with additional features designed to prevent loosening. Their actual ability is questioned and concretely examined. Seven types of those so-called anti-loosening nuts which are readily available in the market are compared with conventional nuts and evaluated their ability, including their manoeuvrability. Two types of loosening devices are developed for this purpose. One is to loosen fasteners by forcing a fastened material. to displace and the other by applying high acceleration to a whole structure. The conclusions obtained are as follows: (1) Nuts with edged spring at the bottom, nylon inserted nuts, metal inserted nuts and rings with sharp inner edge to cover nuts are all unable to stop loosening. (2) A nut with serrated flange at the bottom has the ability to suppress the initiation of loosening to some extent. It makes the fastener resistant to higher levels of acceleration than fine screws. (3) A pair of double nuts and a combination of a nut with an eccentric external taper and a nut with an internal taper can slow the loosening process considerably. The latter may be an answer at present, but it is effective only under limited conditions.