The heat number is contained in the designation of the candle. The designation is deciphered as follows:
BOSCH spark plugs
Example
1 W = thread M14x1.25 with flat sealing surface, wrench size 21 mm; F = thread M14x1.25 with flat sealing surface, wrench size 16 mm; M = thread M18x1.5 with a flat sealing surface, wrench size 25 mm; H = thread M14x1.25 with conical sealing surface, wrench size 16 mm; D = thread M18x1.5 with conical sealing surface, wrench size 21 mm;
2 Heat number. The scale of glow numbers has a range from 06 ("cold") up to 13 ("hot"). In this case, the number 7 corresponds to the previous designation 175, 6 - 200.5-225, etc.
3 A = thread length 12.7 mm, normal spark position; B = 12.7 mm thread length, spark extended; C = thread length 19 mm, normal spark position; D = 19 mm thread length, spark extended; DT = 19 mm thread length, spark extended, 3 ground electrodes; L = thread length 19 mm, spark position significantly advanced;
4 = material of the center electrode. Cr-Ni alloy (Cr-Ni = chromium-nickel), C = Ni-Cu - alloy (Ni-Cu = nickel-copper), S = silver center electrode, P = platinum center electrode - standard spark plug with heavy duty center electrode.
5 R = 1 kΩ, damping resistance.
BERU spark plugs
Example
1 Thread diameter, here M14x1.25
2 F=flat fit, K=cone fit.
3 Heat number, the decoding is the same as for Bosch candles.
4 Thread length, decoding is the same as for Bosch candles.
5 Center electrode material: U=Ultra (Ni-Cu alloy), S = silver center electrode, P = platinum center electrode, O = reinforced center electrode.
6 R = 1 kΩ, damping resistance
Recommended spark plugs for bmw 3-series vehicles from September 1990
1 Non-adjustable triangular ground electrode.
Attention: Given the constant technical progress, it may be that other types of spark plugs can be installed on older cars. Therefore, it is recommended to obtain information about the admissibility of installing one or another type of candles at the service station.