Ever cross-threaded a spark plug? Trust us, it sucks. You generally have to heli-coil ’em since you can’t re-tap it because you risk dropping bits of metal into the engine — until now. These expandable spark plug socket rethreaders from MAC Tools slip past the damaged threads then expand to engage them, allowing you to “chase” the threads from the bottom up. Debris comes up and out with the rethreader.
This is most definitely a specialty tool, but like all specialty tools, when you need it, you need it bad. This could really pull your acorns out of the fire if you (or one of your techs) is a little overzealous installing plugs.
MAC sells ’em in a three-piece set that fits common sizes — 10 mm, 12 mm, and 14mm — for $90. They also sell the less-common 18 mm version separately. You can pick ’em up online or (of course) via your friendly neighborhood tool truck.
3-Pack Expandable Spark Plug Socket Rethreaders [MAC Tools]