The fit sheet included with your BaseClip will indicate if it is the front or rear, see attached example. Look at the column to the right of the Max LBS column you will see the BaseClip number (ex:BC102) listed, this is the front clip.
Now look for the column labeled T1, to the right of this you will see another BaseClip number (ex:BC139) listed, this is the rear clip.
Don't have the clip fit sheets, or need more information? Go here and enter the year, make and model of your car you will have access to all fit measurements, notes, diagrams and in many cases photos of the fit.
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