Spark Plug Cylinder Head Rethreader Kit – 14-Millimeter can save the cost of a new head by repairing damaged threads on aluminum heads. The kit includes a slim design tap and reamer, as well as 2 each; 3/8-inch, 7/16-inch, 0.5-inch and a 0.75-inch inserts. Heavy-duty construction allows for strength and durability. Whether tuning up your ’68 Corvette