  We collect multi-wavelength measurements of the nuclear emission of 20 low
luminosity FR I radio-galaxies to test the viability of the FR I - BL Lac
unifying model. Although poorly sampled, the Spectral Energy Distributions
(SED) of FR Is are consistent with the double peaked shape characteristic of BL
Lacs. Furthermore while the distribution of the FR Is in the broad-band
spectral index planes shows essentially no overlap with the regions where HBL
and LBL are located, this can be simply due to the effects of relativistic
beaming. More quantitatively, deriving the beaming Doppler factor of a given
radio-galaxy from its X-ray luminosity ratio with respect to BL Lacs with
similar extended radio luminosity, we find that i) the luminosity in all bands,
ii) the value of the spectral indices, iii) the slope of the X-ray spectrum,
iv) the overall SED shape, may be all simultaneously reproduced. However, the
corresponding jet bulk Lorentz factors are significantly smaller than those
derived for BL Lacs from other observational and theoretical considerations.
This suggests to consider a simple variant of the unification scheme that
allows for the presence of a velocity structure in the jet.
