27 What does the Bosch spark plug number mean?
Description
This article is from the VW Technical FAQ, by with numerous contributions by Jan Vandenbrande others.
27 What does the Bosch spark plug number mean?
A: For example: WR7DTC
W = Diameter (?) W= 14 mm (?)
R = Resistor (Radio interference suppression, not vital(?))
7 = Heat Range (lower numbers = colder plugs)
D = Length (?)
T = Tri-cathode. If missing, single cathode
C = Copper Anode
Other values, Missing = Carbon, S = Silver, P = Platinum
0 = Final character, Special Electrode configuration (see below)
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