The proper fitting nozzle is based on the shape of your tailpipe.
Measure the outside dimension (O.D.) to determine the width of the tailpipe.
To figure out how the adapter will fit on to the tailpipe it's important to note how the tailpipe/tailpipes protrude from the vehicle.
Older vehicles feature a tailpipe that protrudes from the body and requires a spring-clamp attachment while newer vehicles feature flush tailpipes that require a suction-cup attachment.
Y-connectors are required to connect dual tailpipes.
Starting at the tailpipe, take down an accurate measurement of the distance to the outside.