NGK Sparkplug Codes

Following is a brief list of various codes found in the NGK spark plugs. This is actually a copy of a document that used to be on the Motorcycle Tuning Resources page. Those pages are apparently down so I decided to post the codes here on the TL pages.

Example NGK codes:
[B]  [P]  [6]  [E]  [S]
[D]  [8]  [E]  [S]  [-]  [L]

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
Hottest
10
Coldest

Field four:  Thread reach
E
19 mm
F
tapered seat
H
12.7 mm (1.5")
L
11.2 mm (7/16")
If this 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 center electrode

Field six(after the dash):  Wide gap
8
.032"
9
.036"
10
.040"
11
.044"
13
.050"
14
.055"
15
.060"
20
.080"
L
Half heat range
N
Special ground electrode (note: appears to be limited to BMWs)
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Last modification February 16, 2003		 kailasmall.gif 2kB

NGK Sparkplug Codes