The Radiators on many cars have different size tanks which are supported by different  insulators. 

      This is specifically for 1966-early 76 Corvettes.. as shown.   

      Normally this insulator is used on the upper & lower tank clamping the radiator tank area between the fan Shrould and the radiator tank join.. and note the it has ONE locating nib only.

     For closely related years of Corvette Applications note first the thickness of the tank up against this picture.