This is what an aluminum head looks like after a bolt or in this case an exhaust stud strips out. The cobble repair is to use an American (SAE) coarse thread bolt that is larger and will "self-tap" new threads into the aluminum. The correct method is to install a Heli-Coil stainless steel thread insert.

Using the recommended size drill bit, the hole is enlarged and cleaned up.

These are the parts of the typical Heli-Coil installation setup. Top to Bottom: Stainless steel inserts, tap, insert installation tool.

Now the hole has new threads ready to accept the Heli-Coil insert.

The insert is threaded onto the end of the installation tool. Note how the inserts "tang" is hooked against one of the raised lands of the tool end. Also note the notch opposite the tang to allow easy removal of the tang after installation.

The insertion tool w/insert is threaded into the hole.

The insert is threaded into the hole until the end (red circle) is just below flush. Note the position of the tang (red arrow). Now insert a punch smaller than the hole and place the flat end of the punch on the bend of the tang (blue arrow) and hit it with a blow, shearing off the tang. In this case removal of the tang isn't necessary.

Double nut the exhaust stud as shown and install the stud, threaded into the hole until it is quite snug. To remove the nuts, hold the bottom nut with a wrench in your palm and the top nut wrench in your fingers of the same hand. Have the top wrench offset one flat and squeeze the two wrenches together, using your fingers to pull the top wrench towards you (which should be in the direction to loosen the top nut, in this case it is from left to right) and the top nut will "break free" and then both nuts can be removed with your fingers.