A method for manufacturing an apparatus for measuring flow of a fluid flowing through a measuring tube of metal using the magneto-inductive principle, comprising the method steps as follows: securing first and second collars of metal externally on the measuring tube with an orientation perpendicular to the tube axis of the measuring tube lining the measuring tube internally with an electrically non-conductive, elastic liner and altering a measuring section of the measuring tube located at least partially between the first collar and the second collar by means of cold deformation in such a manner that the cross sectional area of the measuring section is reduced compared with the cross sectional area of an inflow section of the measuring tube located upstream from the measuring section and an outflow section of the measuring tube located downstream from the measuring section.