This nut (1) comprises a nut main body (3) having a substantially cylindrical shape and constituted by a plurality of nut segments (3a), an outer cover (4), a restraining ring (5), an inner cover (6) comprising a restraining plate (6a) at one end portion of the inner cover (6) and serving to cover an outer circumference of the nut main body (3), and a ring-shaped spring (7) serving to bias the nut main body (3) to cause the nut main body (3) to expand radially. Protrusions (8) protruding in a circumferential direction are formed on an inner surface of the inner cover (6). Grooves (9) are formed on an outer surface of the nut main body. The protrusions (8) and the grooves (9) have slant surfaces (10) that contact each other on the same side in the axial direction.