The glow number is contained in the designation of the spark plug. The designation is deciphered as follows.
Bosch spark plugs
- 1 W - thread M14x1.25 with a flat sealing ring, wrench size 21 mm.
- 2 F - thread M14x1.25 with a flat sealing ring, wrench size 16 mm.
- 3 M - thread M18x1.5 with a flat sealing ring, wrench size 25 mm.
- 4 N - M14x1.25 thread with conical sealing ring, wrench size 16 mm.
- 5 D - thread M18x1.5 with a conical sealing ring, wrench size 21 mm.
(2) R - with resistance to protect against interference. The operation of the ignition system from the presence of resistance does not change.
(3) - heat number. The scale of numbers is indicated from 05 ("cold") up to 13 ("hot"). In this case, the designation 7 corresponds to the old heat number 175 (early designation), 6 - 200, 5 - 225, etc.
(4) A - thread length 12.7 mm, normal spark position.
B - thread length 12.7 mm, closed spark position.
C - thread length 19 mm, normal spark position.
D - thread length 19 mm, closed spark position.
(5) - material of the central electrode: Cr-Ni alloying, C - central electrode made of NiCu alloy, S - silver central electrode, P - platinum central electrode, O - standard candle with reinforced electrode.
By means of a copper core in the central electrode, and even more so by means of a silver central electrode, the thermal conductivity and thus the heat dissipation are increased. The advantage of a spark plug with a platinum center electrode is high flammability as well as low wear and a larger heat transfer area.
Beru spark plugs
- 1 - thread diameter in mm, here M14x1.25.
- 2 - structural designation, e.g. K - for tapered fit, R - for anti-interference resistance.
- 3 - glow number (like Bosch).
- 4 - thread length (like Bosch).
- 5 - electrode material, for example. V - for copper.
Deviate from the factory-recommended heat numbers only when operating conditions deviate significantly from normal and production problems appear. If the candles are constantly covered with soot, then it means that the self-cleaning temperature is not reached (only for short distance driving), then candles with the next upward glow number are recommended. If the engine is used exclusively at full throttle, then candles with the next decreasing glow number can be used.