A lock nut device consists of a lock nut (22) and a lock spring (31). The spring is bent into an U-shape and extends in a axial plane over the nut. It has spring legs (32) lying in grooves (25) in the nut and has end portions formed for engagement with the profile portion (16) on a non-rotatable element (4). In the engagement position, the legs are at such a distance from the nut surface that, with the aid of a socket forced over the nut, they can be pressed towards the nut surface, thus moving the end portion from the engagement position.