NGK Sparkplug coding explained

NGK Spark Plug Codes:

NGK code:  [B]  [P]  [6]  [E]  [S]

Field one:  Thread Diameter
A 18 mm
B 14 mm
C 10 mm
D 12 mm


Field two:  Construction
C Hex size 5/8″
K Hex size 5/8″ with projected tip (ISO)
M Compact type
P Projected insulator type
R Resistor
SD Surface discharge for rotary engines
U semi-surface discharge
Z inductive suppressor


Field three:  Heat Range
2 Hot
10 Cold


Field four:  Thread reach
E 19 mm
F tapered seat
H 12.7 mm (1.5″)
L 11.2 mm (7/16″)
If this field is blank, an 18 mm diameter plug has 12 mm reach; and a 14 mm plug has 9.5 mm (3/8″) reach.


Field five:  Firing and construction
A,B Special design (no details given)
C special ground electrode
G Racing use
GV Racing V-type
H Half thread
K 2 ground electrodes
L Half heat range
LM Compact lawn mower type
M 2 ground electrode for Mazda rotary engine
N Special ground electrode
P Platinum tip (premium)
Q 4 ground electrodes
R Delta ground electrode for BMW
S Standard 2.6 mm electrode
T 3 ground electrodes
V Fine-wire electrode, gold-palladium
VX Platinum tip (high performance)
W Tungsten electrode
X Booster gap
Y< V-groove centre electrode


Field six:  Wide gap
8 .032″
9 .036″
10 .040″
11 .044″
13 .050″
14 .055″
15 .060″
20 .080″

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