Here are 5 Star insulators with the following measurements: The third number is the width of the insulator at the wire groove. (L->R) #684 4.125"x3.25"x2.65" #686 4"x3.125"x2.38" #687 4"x3.125"x2.33" #688 3.95"x3.125"x2.33" #821 4"x3.25"x2.65" I am having trouble deciding on the CD#s for these insulators. Your help would be appreciated.