The interference of Bessel beams, analysed hitherto only for the case of two superposed beams, is generalized onto the case of multiple beams. In this way a counterpart of diffraction grating for radial geometry can be created and axial intensity distribution becomes analogous to the grating factor, Le., the far diffraction pattern due to interference of multiple linear slits. Peaks corresponding to different diffraction orders are spaced equally along the optical axis. A kind f optical ruler can be obtained in this way.