One of the most widespread models of electrons drifting around the cathode in magnetrons is the single-stream state, which is the Brillouin stream with purely azimuthal motion. We describe a single-stream state in which electrons not only move in the azimuthal direction, but also along the axial direction, which is useful for consideration, for example, of relativistic magnetrons, MILOs, and coaxial transmission lines. Relations are given for the conditions of magnetic insulation for 2D electron motion, for 1D azimuthal and axial motion, and for synchronism of these streams with the operating waves of M-type microwave sources. Relations are also provided for the threshold of generation in magnetrons with 2D electron motion.