A nut is employed to fix a faucet on a wash basin or a kitchen basin and contains an external driving member and an internal screwing member. The external driving member includes a cylindrical fence, an accommodating cavity, a first edge, and a second edge; the cylindrical fence has at least one limiting block and a griping face. The internal screwing member is fitted into and retained with the accommodating cavity and includes an annular cliff, a through orifice, a third edge, and a fourth edge; the annular cliff has plural slots longitudinally extending and isometrically arranged to the fourth edge from the third edge so as to define a plurality of flexible retaining portions, each having an inner threaded section; the annular cliff also has at least one longitudinal recess for retaining with the at least one limiting block of the external driving member and has a contacting fringe.