http://www.emhart.com/products/helicoil.html

While working on getting the car put back together, I just found yet another reason to hate the previous owner's mechanics. I went to tighten up a bolt and found that it was stripped. After taking a closer look, I found that the original bolt had apparently been stripped or lost, and they replaced it with a different one. The original one had been a metric fine thread hardened bolt. The one that they used was a larger diameter non-metric coarse thread weaker grade bolt. Besides that, it was shorter than the original one was, and they stripped both it and the threaded hole.
You may be wondering if they'd do something like this on an important part.
Yes they would. This is a bolt holding on a lower control arm. I found this problem less than five minutes after repairing a stripped engine mount bolt, that was probably caused by the same %^&()+|*@!^%$~`-/. I'm not sure how I'm going to fix this yet, because I'd kind of like to use the original size bolt. I don't know if I'd trust something like a Helicoil in there, especially since the ones I've seen are pretty short.
Mike Schmidt

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Hi Mike,

Just used a helicoil kit for a stripped bolt hole in my water thermostat housing with great results. I had to stack two coils on top of each other, cutting off the top one flush with the surrounding surface. Couple of tips, bring the bolt with you to get the proper size kit and make sure you tell the seller that it's metric. I got my kit from the local NAPA dealer. Make sure you have the right size drill bit needed for the kit and make sure it's sharp. While at the store get a tap handle if you don't have one. It will make the tapping of the new hole go smoothly and straight. The little tang that is used to insert the coil is easily broken off by using a punch that is a little smaller than the inner diameter of the coil. The punch end should have sharp edges, place against the tang and hit it square with a small hammer. Do not use a nail or other device since you might push the tang to one side and muck up the coil. The repair I did worked fine, the bolt threaded in with no problems and I cinched it down pretty well.

Good luck,
Constantine

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Helicoil Wire Thread Inserts

HeliCoil Inserts provide positive means for protecting and strengthening all tapped threads. They are mirror-smooth, reinforced internal threads of cold rolled 18-8 stainless steel, or other space age material, with hardness far in excess of the usual tapped materials.

The outstanding engineering features of HeliCoil Inserts, long recognized by the leading aircraft, industrial and military equipment manufacturers, have established their widespread use in these fields. The many company standards and defense specifications for HeliCoil Inserts also prove their wide acceptance.

Helicoil Free Running Inserts

	HeliCoil Inserts are manufactured from High Tensile Stainless Steel Wire which has been formed into a diamond section of exacting standards. When installed the HeliCoil provides a precision female thread of high surface finish and strength.
	Installation of the HeliCoil is achieved by means of the Driving Tang, which is removed after assembly. To permit the removal of the Tang a Notch is cut into the section to provide a shear point. The design of the notch allows for bolt entry from EITHER END of the HeliCoil.
Insertion of the HeliCoil is achieved using the appropriate Installation Tool. The driving tang is engaged in an abutment or slot in the tool and pre-wound into the nozzle. Placing the tool over the correctly tapped hole, further winding will install the HeliCoil to the correct depth. After withdrawal of the tool the tang is removed to allow the bolt or screw to pass through the insert.
	Once fitted the HeliCoil will not move. It is secured in position through Radial Pressure exerted by the coils on the thread flanks. Radial pressure exists due to the outside diameter of the HeliCoil in its Free State being larger by a calculated amount than the hole into which it is to be installed.

Helicoil Screw-Lock Inserts

	In addition to all the characteristics of Free Running inserts the HeliCoil Screw-Lock insert has the unique feature of one or more of its intermediate coils are deformed polygonally. This serves to create strong resilient pressure onto the thread flanks of the bolt as it passes through. This in-built Prevailing Torque of the GRIP COIL positively locks screws and bolts safeguarding against loosening under vibration and impact.
Screws can be inserted by hand up to the grip coil, after which some mechanical means must be employed to overcome the locking medium. HeliCoil Screw-Lock inserts are coloured RED for identification only, to distinguish them from Free Running inserts. A C.O.S.H.H. sheet is available for the Dye upon request. To obtain the best performance from HeliCoil Screw-Lock inserts it is recommended that only good quality close limit fit, rolled thread, oil lubricated screws or bolts are used. On no account should sub standard or "Black" bolts (with heat treatment scale) be used with HeliCoil Screw-Lock inserts. When using Unplated, Heat Treated or Stainless Steel screws with HeliCoil Screw-Lock inserts and Anti Seize Compound (such as Molibdenum Disulphide) should be applied (preferably to the screw) to minimise galling and maximise cycle life. Locking Compounds Under no circumstances should thread locking compounds be applied to the assembly. This will almost certainly cause the HeliCoil to withdraw.

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Maybe even better solution is this Timesert thread repair.

https://www.timesert.com/