Non-return block for snow chains

A non return block (5) for locking a tensioning terminal portion (7) of snow chains (2), comprising a body (51) which defines a channel (12) in which the terminal portion (7) passes and a ratchet or a pawl (13) pivoted on the body (51) to lock the terminal portion (7) is described. The non-return block comprises at least one insert (62, 63) of soft material fixed to the body (51) of the non-return block so as to protrude laterally therefrom to come into contact with the rim (8) of the wheel of the vehicle, avoiding deterioration thereof through rubbing.