NGK Spark Plug Codes

NGK spark plug codes generally consist of six fields, which break down as follows: [B C] [P R] [6] [E] [S] - [11]. Some fields (e.g., the second field) are optional, and some fields may have multiple letters.

Field one: Thread Diameter and Wrench Size

	Thread dia.	Hex socket
A =	18.0mm	25.4mm
B =	14.0mm	20.6 or 20.8mm
C =	10.0mm	16.0mm
D =	12.0mm	18.0mm
E =	8.0mm	13.0mm
G =	PF 1/2	23.8mm
AB =	18.0mm	20.6 or 20.8mm
BC =	14.0mm	16.0mm
DC =	12.0mm	16.0mm
BM-F =		16.0mm
B-F =		16.0mm
A-F =		20.8mm
BK =	ISO type of BCP

Field two: Spark Plug Shape L = short type M = compact type (hex. 19mm) P = projected insulator type R = resistor type U = surface or semi-surface discharge Z = inductive suppressor

Field three: Heat Rating

2 = "hot" to 14 = "cold" (See Heat Range Chart)

Field four: Thread Reach

E = 19.0mm
H = 12.7mm (1.5")
L = 11.2mm (7/16")
EH = half thread (19.0mm total; 12.7mm threaded)
None = A type: 12.0mm; B, BM, B-F types: 11.2mm; G type: 22.5mm; A-F type: 10.9mm; B-EF types: 17.5mm; BM-F type: 7.8mm

Field Five: Firing and Construction

A, B, D, Z = special design (no details given)
C = short ground electrode
F = tapered seat
G = fine-wire center electrode, nickel
J = 2 ground electrodes (special shape)
K = 2 ground electrodes for certain Toyotas
-L = half heat range
-LM = insulator length = 14.5mm
M = insulator length = 18.5mm
-N = special ground electrode
P = platinum tip
Q = 4 ground electrodes
R = delta ground electrode S = super copper core
T = 3 ground electrodes
V = fine-wire centre electrode, gold palladium
VX = platinum center electrode
W = tungsten electrode
X = booster gap
Y = v-grooved center electrode with extra projection

Field Six: Spark Gap (from factory)

8 =	0.8mm	0.032"
9 =	0.9mm	0.036"
10 =	1.0mm	0.040"
11 =	1.1mm	0.044"
13 =	1.3mm	0.050"
14 =	1.4mm	0.055"
15 =	1.5mm	0.060"
20 =	2.0mm	0.080"
None =	Std. gap

Copyright © VSource.org 1999-2005 [Sources: Robyn Landers; 2001 NGK (UK) Motorcycle Applications Catalog; see also NGK USA]