The tap gradually cuts the 12mm thread, slightly wider so that the thread is cleaned up, and you can fit the machined aluminium insert into the spark plug hole. If you have a cross threaded 12mm x 1.25mm spark plug in an Aluminium head, then this is the perfect little kit to rectify it.
This product would be ideal for mechanics and DIY enthusiasts looking to efficiently repair worn-out spark plug threads in 12mm aluminum heads for their vehicles.
