Here is a good, lightly-used K-D No. 730 Spark Plug Hole Thread Chaser. It has the 2 most common 14mm & 18mm sizes.
K-D Tools 14-18mm Thread Restoring Tap Rethreader Mod 730 Spark Plug Opening USA
KD Tools - Spark Plug Gap Gauge 0.025"-0.045" Usa Mechanic Tool Auto
KD Tools - Spark Plug Gap Gauge 0.020"-0.100" 3293 new
KD 2127 Spark Plug Thread Inserts 14mm Long (7/16")
ACE Professional Metric Spark Plug Re Thread Set (855414 No. 40) w/ KD 730 Tool
K-D TOOLS SPARK PLUG THREAD CHASER 14 & 18 MM RETHREADER 730, 901, Etc USA MADE