Weight: 0.17The term "indexing" when referring to spark plugs, is the process of adjusting the spark plug electrode to the correct position in the combustion chamber. More complete combustion and consequently more horsepower is developed by indexing the electrode gap toward the center of the piston, favoring the exhaust side if possible.AccelCopper Indexing Washers Assortment KitFits all models with 14mm spark plugsIncludes (10) .043", (10) .054" & (10) .064" thick washersEach increment of washer size changes the final angle of the ground electrode by 100°By: HOLLEY PERFORMANCE PRODUCTS,INC.