The sales symbol on a spark plug is composed of a basic"Heat Range" number with letters and numbers to indicate major features of the plug design. Theres chars contain a detailed example of the Champion Sales Symbol.

R
V
15
Y
C
4
SUPPRESSOR / SHIELDING
Letter Description
E
Shielded 5/8" - 24
H
Shielded 3/4" - 20
K
Resistor (Special Application
M
Shielded 5/8" - 24 Ordnance
R
Resistor
T
13/16" - 20 thread Above Hexagon
U
Auxiliary Gap
X
Resistor (Special application)
SHELL DESIGN
Letter
Thread Size
Reach
Hex
B 18mm 13/16" 7/8"
C 14mm 3/4" 5/8"
D 18mm 1/2" 7/8"
GC* 7/8" - 18 All 7/8
GM* 18mm All 7/8"
H 14mm 7/16" 13/16"
J 14mm 3/8' 13/16"
L 14mm 1/2" or .472"
13/16"
M 18 1/2" 7/8"
N 14mm 3/4" 13/16"
S 1-1/8" 5/8" 1"
W 7/8" - 18 All 15/16" or 1
X 14mm 1/2" or .500" 5/8"
HEAT RANGE / APPLICATION
Ref.# Description
1-25 Automotive, small engine or ordnace
75-99 Industrial & Special Application
FIRING END DESIGN
Letter
Description
B
Two Ground Electrodes
C
Copper Plus Design
D
Protruding Nose, Round Ground Electrode
F
Three Ground Electrode
G
Fine Wire-Semi Precious Electrode
J
Cutback Ground Electrode, Includes Modified Gap
N
Four Ground Electrode
P
Platinum Electrode
R
Push Wire
Y
Standard Projected
*PP
Double Platinum
*PYP
Projected Double Platinum
*WP
Iridium/Platinum
WPC
Iridium/Platinum/Copper
WPCC
Iridium/Platinum/Double Copper
SPECIAL GAP DESIGNATION
No.
Description
15
Gapped at .015"
17
Gapped at .017"
21
Gapped at .021"
25
Gapped at .025"