US Patent 6905142 Hydraulic coupling

An improved hydraulic coupling includes a fitting and a nut that are threadably connectable together. The fitting includes a generally annular groove having a lateral frusto-conic engagement surface. The nut includes a plurality of elongated fingers that each include a projection having an outwardly-disposed edge. When the coupling is assembled, the edges are frictionally engaged with the engagement surface as a result of the elastic deflection of the fingers. The frusto-conic shape of the engagement surface provides progressively greater frictional resistance in a direction of unthreading of the coupling, whereby loosening of the coupling during operation of the fluid circuit is resisted.