Tap is designed for aluminum heads only. Set includes 4 inserts and thread locking compound. This kit repairs damaged 14mm spark plug threads It's simple to use, simply open spark plug hole with reamer/tap. Screw insert onto spark plug. Use spark plug socket to install spark plug and insert. Remove spark plug and check that insert is properly seated. Set includes 1 each of 4 inserts (3/8, 7/16, 1/2, and 3/4 reach) and thread locking compound.
