We investigate the brightest regions of the kpc-scale jet in the powerful radio galaxy 3C 346 , using new optical Hubble Space Telescope ( HST ) ACS/F606W polarimetry together with Chandra X-ray data and 14.9 GHz and 22.5 GHz VLA radio polarimetry . The jet shows a close correspondence in optical and radio morphology , while the X-ray emission shows an 0.80 \pm 0.17 kpc offset from the optical and radio peak positions . Optical and radio polarimetry show the same apparent magnetic field position angle and fractional polarization at the brightest knot , where the jet undergoes a large kink of almost 70 degrees in the optical and radio images . The apparent field direction here is well-aligned with the new jet direction , as predicted by earlier work that suggested the kink was the result of an oblique shock . We have explored models of the polarization from oblique shocks to understand the geometry of the 3C 346 jet , and find that the upstream flow is likely to be highly relativistic ( \beta _ { u } = 0.91 _ { -0.07 } ^ { +0.05 } ) , where the plane of the shock front is inclined at an angle of \eta = 51 \pm 11 degrees to the upstream flow which is at an angle \theta = 14 _ { -7 } ^ { +8 } degrees to our line of sight . The actual deflection angle of the jet in this case is only 22 degrees .