1989 Ski-Doo Repair Manual, Page 378Get this manual
Section 04
ELECTRICAL SYSTEM Sub-section 03 (SPARK PLUGS)
DESIGN SYMBOLS USED ON NGK SPARK PLUGS
First letter prefix for thread and hexagon size Secondthird letter prefix for construction feature, except single prefix Heat rating number First letter suffix for thread: reach Second letter suffix for construction feature, etc
Thread size
Hexagon size
Construction feature
Thread reach
Construction featureetcB
Hexagon size 20.6 mm
Hexagon size 16.0 mm
Hexagon size 23.8 mm
12.0 mm (thread ia18 mrn) 9.5 mrn (thread dia14 mm)
Specials
Special plug for Honda vehicles