An approach for obtaining one-way transmission in the beaming regime is suggested that is based on the directional radiation of surface plasmons in nonsymmetric metallic gratings with a single slit. In contrast to the various nonsymmetric one-way diffraction gratings that have recently been proposed, the possibility of obtaining of narrow beams is demonstrated. Strong directional selectivity can appear a wide range of the observation angles, while the angle of incidence is retained.