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The various numbers and letters in a spark plug code or identification number basically identify the features and functions of a particular plug. Included would be information such as plug type, heat rating, construction, thread diameter, thread reach and firing end construction. Most of these are irrelavant for RDs but it's always handy to have this memorised. Honest! The code can be broken into 6 parts : B CPR 8 E S - 11 |
Field 1: Thread diameter.
A: 18mm
B: 14mm
C: 10mm
D: 12mm
J: 12mm
Field 2: Construction. One or more letters may be combined.
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 3: Heat Rating.
2: hot, up to 11: cold.
Field 4: Thread reach.
E: 19mm (3/4")
EF: 19mm tapered seat
H: 12.7mm (1.5")
EH: Partial thread - 12.7mm total thread, 19mm total reach
L: 11.2mm (7/16")
S: 9.5mm (3/8")
Z: 21mm
If this field is blank, an 18mm diameter plug has 12mm reach, and a 14mm plug has a 9.5mm (3/8") reach.
Field 5: Firing end construction.
A: special design
B: special design
C: low angle ground electrode
CM: Compact type, low angle ground electrode
E: V Groove centre electrode (14mm only)
ES: Standard 3/4" thread reach (2.5mm) centre electrode
F: Tapered seat G: Fine wire nickel alloy centre electrode
G-G: Copper core ground electrode
GV: Gold-Palladium centre electrode, V type racing use
K: 2 ground electrodes for certain Toyotas
L: half heat range
LM: compact lawn mower type
M: 2 ground electrodes for Mazda rotary engine
N: special side electrode
P: platinum tip (premium)
Q: 4 ground electrode
R: special ground electrode
S: standard 2.5mm centre electrode
T: 3 ground electrode
V: fine-wire centre electrode, gold palladium
VX: high performance platinum tip
W: tungsten electrode
X: booster gap
Y: v-groove centre electrode
Z: Thick 2.9mm centre electrode
Field 6: Wide gap .
8: 0.8mm / .032"
9: 0.9mm / .036"
10: 1.0mm / .040"
11: 1.1mm / .044"
13: 1.3mm / .050"
14: 1.4mm / .055"
15: 1.5mm / .060"
20: 2mm / .080"