A life saver
Your review: Had Spark plug blow out of head on my 70 VW. It had already been repaired with an 16mm insert. This insert allowed me to tap to an 18mm thread,and use the correct standard spark plug. This device saved me from having to buy and install a new cylinder head.
Pros: Has super duty thread locker already on it. Easy to install. Robust construction.
Cons: None that I can think of