Securing nut including a nut body and straining ring

A securing nut comprising a nut body and a straining ring rotationally arranged on the nut body, the nut body having a neck, the straining ring being shoved onto the neck of the nut body and reversibly secured thereto by clamping, an inner surface of the straining ring having at least two grooves, each of the at least two grooves being a circular arc, the at least two grooves cumulatively extending across an entire angular range of 360°, an outer surface of the neck having a plurality of cams corresponding in number to the number of grooves, each cam being associated with a groove and extending across an angular range which is different than that of the associated groove and less than 60°, wherein said neck has a continuous inner surface with a contour which is elastically reversibly deformable between a round contour and a non-round contour by compression of said neck by rotation of said straining ring and uncompression of said neck by further rotation of said straining ring.