Abstract: A detachable fixing device for engaging a bolt comprises a nut and a lever pivotally attached to the nut. The lever is provided with two lugs, whereas the nut comprises two articulated, threaded and spring-biased bolt grips. In a home position of the lever, the grips are moved apart to allow the loose slipping of the nut onto the bolt. In an active position of the lever, the grips are pressed on by the lugs, whereby the bolt grips engage the bolt with the thread.