Had to replace the Helicoil on a cylinder after the insert was torn out attempting to chase the threads with the crap ATS 20200 chaser which is about 10 thousands larger than a new spark plug. Threw the chaser in the trash and ordered two of these in case things didnt work out and it was a good thing! These are sized nearly perfectly for narrow or wide deck cylinders so if your depth stop is set slightly too long you could insert it into the cylinder and need to rip it out and try again. I recommend setting the depth stop a couple of threads shorter than your spark plug, then removing the stop and turning the bare insertion tool while visualizing the stakes so you can position the Helicoil precisely where you want it to stop. Didnt have a very expensive aircraft Helicoil staking tool so used red Loctite when inserting in case plier staking isnt sufficient.

Did not work, too large. Needed smaller diameter which wasn’t available through Spruce.

Jason B Verified Purchase

Heli-Coil Insert 18MM X 1/2

Spark plug heli coil. Quick shipping and worked as desired.

David M Verified Purchase

Heli-Coil Insert 18MM X 1/2

Perfect ! Thanks a lot !

Jean-louis B Verified Purchase

Heli-Coil Insert 18MM X 1/2

Order came in timely fashion. Part broke on install. Ordered 3 more. Those came in timely fashion. Do not attempt this install without the proper tool.

Chris H Verified Purchase

Heli-Coil Insert 18MM X 1/2

For long reach plugs - use a tool that’s in good condition and make sure the threads are clean and oiled

Evergreen A Verified Purchase

Heli-Coil Insert 18MM X 13/16

Worked fine.

Melvin D Verified Purchase

Heli-Coil Insert 18MM X 1/2

This is the real deal for aircraft engines, but dont think you can just thread it in easily. Use the Helicoil insertion tool AFTER youve carefully run the Helicoil stepped tap, with lots of aluminum cutting fluid or grease on it, through the spark plug hole, repeatedly until it theres little resistance to turning it. MAKE SURE THE PISTON IS NEAR THE BOTTOM! Put the coil in the insertion tool with about one thread of the coil exposed and hold the tool inner shaft and outer sleeve so the exposed coil is wrapped tightly to the inner shafts threads. Get the tool centered on the hole and square with it (do this more by feel than sight). Then slowly rotate the entire tool without allowing the coil to loosen from the threads on the inner shaft. It will probably take many tries, so be patient, its never easy with airplanes. Dont be afraid of removing the coil from the tool and starting over, just be very careful with the coil so you dont distort it or break the tang off. Once the coil gets threaded into the cylinder, hold the outer sleeve and turn the inner shaft until the coil clears the outer sleeve, then screw the coil so the end of it is about one thread inside the hole. Unscrew the inner shaft from it and inspect. If it looks good, use a long needle nose pliers to grab the end of the tank and wiggle it in and out about 1/16 until it work hardens and breaks off. DONT DROP IT INSIDE THE CYLINDER! Then you need the staking tool to drive the serrated end of the coil into the cylinder head, to lock it in place. Otherwise, it will screw out with the sparkplug the next time you remove one. USE SPARKPLUG THREAD LUBE (black liquid) AND A FRESH OR ANNEALED WASHER WHENEVER INSTALLING A SPARKPLUG! Silver anti-seize goop is NOT sparkplug lube...

Gelston A Verified Purchase

Heli-Coil Insert 18MM X 1/2

Quality product - works as intended. May look oversized when you get it but it has to be to install, fit, and seat properly.

Integrity A Verified Purchase

Heli-Coil Insert 18MM X 13/16

The low reviews on this page come from not knowing how to insert the helicoil. The helicoil looks too big, but with a special tool, it is inserted into the cylinder with a bit of spring tension so that when you pull the tool out it is wedged in there.

Fit perfectly. Understanding how the installation tool works is critical! I used a NAPA Balkamp 18-1.50mm spark plug thread repair kit P/N 770-3066.

Size .5mm off. Material possibly to thick. Could not use. Might work for non-aircraft use.

We ordered an 18 mm helicoil for a Lycoming engine. The Helicoil came in a bag labeled 18 mm but definitely was not 18 mm. it measured more than 20 mm on the ID. We had an additional 2 days down time on this engine while we procured the correct helicoil.