2005 Ski-Doo Racing Handbook, Page 153Get this manual
SECTION 05ENGINE PREPARATION
Design Symbols Used on NGK Spark Plugs
First letter prefix for thread and hexagon size Letter Thread size 18 mm 14 mm 10 mm 12 mm 78 in-18 PF 12 in-14 Hexagon size 25.4 mm 20.6 mm 16.0 mm 18.0 mm 23.8 mm 23.8 mm Second and third letter prefix for construction feature, except single prefix Letter Construction feature Hexagon size 20.6 mm Hexagon size 16.0 mm Hexagon size 23.8 mm Compact type (SHORTY) Compact type (BANTAM) Projected insulator nose type Resistor type Shielded type Surface discharge type (85) (95) 10 (105) Racing plugs 11 12 13 14 Colder type Ordinary plug Heat rating number Hotter Type First letter suffix for thread: reach Letter Thread reach 12.0 mm (thread dia18 mm) None 9.5 mm (thread dia14 mm) 22.5 mm (thread diaPF 12 in14 mm) 16.0 mm (thread dia78 in-18mm) 11.2 mm 12.7 mm (racing type 18.0 mm) 19.0 mm (racing type 18.0 mm) Conical seat type -F B-F BMBE10.9 MM 11.2 MM 7.8 MM 17.5 MM Second letter suffix for construction feature, etcLetter GV Construction feature, etc-Specials -Special plug for Honda vehicles -Competition type -Racing plugs, center electrode of nickel alloy -Racing plugs, center electrode of precious metal -Racing plugs, nickel electrode -Racing plugs, platinum ground electrode -Shielded resistor plugs -Copper core center electrode (Super) -Center electrode of precious metal -Tungsten electrode -Series gap plugs -V-Grooved center electrode