  We present a publicly-available spectral model for thermal X-ray emission
from a baryonic jet in an X-ray binary system, inspired by the microquasar SS
433. The jet is assumed to be strongly collimated (half-opening angle
$\Theta\sim 1\deg$) and mildly relativistic (bulk velocity $\beta=V_{b}/c\sim
0.03-0.3$). Its X-ray spectrum is found by integrating over thin slices of
constant temperature, radiating in optically thin coronal regime. The
temperature profile along the jet and corresponding differential emission
measure distribution are calculated with full account for gas cooling due to
expansion and radiative losses. Since the model predicts both the spectral
shape and luminosity of the jet's emission, its normalisation is not a free
parameter if the source distance is known. We also explore the possibility of
using simple X-ray observables (such as flux ratios in different energy bands)
to constrain physical parameters of the jet (e.g. gas temperature and density
at its base) without broad-band fitting of high-resolution spectra. We
demonstrate this approach in application to Chandra HETGS spectra of SS 433 in
its 'edge-on' precession phase, when the contribution from non-jet spectral
components is expected to be low. Our model provides a reasonable fit to the
1-3 keV data, while some residuals remain at higher energies, which may be
partially attributed to a putative reflection component. Besides SS 433, the
model might be used for describing jet components in spectra of other Galactic
XRBs (e.g. 4U 1630-47), ULXs (e.g. Holmberg II X-1), and candidate SS 433
analogues like S26 in NGC7793 and the radio transient in M82.
