Spark Plug Info!
Everything you ever wanted to know about ND & NGK plugs!
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NGK Spark Plug Chart

Example (note that not all 6 fields will always be used, such as in BKR6EY):

B CPR 6 E S -11

First box from example (B):

Letter Thread Diameter

A 18mm

B 14mm

C 10mm

D 12mm

J 12mm

Second box from example (C, P, R):

Letter Construction

C Hex size 5/8"

K 5/8" projected tip (ISO)

M Compact type

P Projected insulator type

R Resistor type

U Surface or semi-surface discharge type

Z Inductive resistor

Third box from example (6):

Heat Range
2 (Hot) <ÉÉÉ> 12 (Cold)

Fourth box from example (E):

Letter Thread Reach

E 19mm (3/4")

F Tapered seat

H 12.7mm (1/2")

L 11.2mm (7/16")

No symbol:
18mmè = 12mm reach
14mmè = 9.5mm (3/8") reach

Fifth box from example (S):

Letter Firing End Construction

A Special design

B Special design for Honda CVCC

C Low angle ground electrode

G Fine wire nickel alloy center electrode

GV Gold-palladium center electrode
Special construction of V-type
Racing use

H Partial thread

K 2 ground electrodes for Toyota / BMW

L Half heat range

LM Compact type for lawn mower

M 2 ground electrodes for Mazda rotary engine

N Special side electrode

P Premium platinum

Q 4 ground electrodes

R Special ground electrode

S Standard 2.6mmè center electrode

T 3 ground electrode

U Semi-surface discharge

V Fine wire gold-palladium center electrode

VX High performance platinum

W Tungsten electrode

X Booster gap

Y V-grooved center electrode

Z Thick 2.9mmè center electrode

Sixth box from example (-11):

Number Gap

-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 2.1mm (0.080")