self - tightening snow chain for attachment to a vehicle wheel to provide traction . the preferred self - tightening snow chain includes a traction cable and a tensioning device including a housing having a top including a set of housing teeth , a bottom and at least one aperture ; a lever interconnected to the housing ; a ratchet spool within the housing having a set of ratchet teeth that mate with the housing teeth and a channel between upper and under surfaces to receive a cord that is interconnected with the ratchet spool ; a tension spring that places a bias on the ratchet spool toward a wind - up direction ; and a wave spring . a preferred tensioning device includes a cord sub - unit having two knobs , one on each end , and a grommet encircling the cord . a method of assembling the tensioning device is also disclosed .