The invention relates in first instance to a nut having a first part (11) which has a first through opening (O1), and having a second part (12) which has a opening (O2) having an opening contour, the parts (11, 12) being connected so as to be rotatable about a rotational axis (A) which passes through the openings (O1, O2), and the openings (O1, O2) being aligned with one another, in addition, the first opening (O1) on its inner face having a profile which extends in the peripheral direction and which is interrupted in the peripheral direction. In order to provide a nut which is quickly mountable on a threaded bolt, and which has a simple design that allows greater security against the nut coming off the threaded bolt, it is proposed that the opening contour of the second opening is non-circular. The invention further relates to a combination of a bolt (4) having a cross-sectional area with a nut (10).