WHAT SIZE SPARK PLUG SOCKET TO USE
Depends on which size plug you are using. Hint, keep changing sockets until you find the one that fits. They are not metric.
There
are three sizes of plug in normal use, 10mm, 14mm and 18mm. (They are
identified by their thread size) The socket sizes for these are 5/8"
(16mm) 13/16" (21mm) and 15/16" (24mm). However, many 14mm plugs (the
most common size) have 5/8 hexagons, and many 18mm plugs have 13/16
hexagons!
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