The dependence of the cross-section and the current distribution on an applied magnetic field in translationally symmetric hybrid systems, in which the magnetic field is produced by external conductors and plasma currents, is considered. If the flux function and the plasma boundary are expanded in Fourier series, this dependence is obtained as relationships between Fourier coefficients. In a first approximation, the cross-section and the current distribution are determined by the applied magnetic field, and for some cases a conducting wall is necessary.