To avoid interference from radio frequencies, the manufacturers use so-called anti-interference spark plug plugs and, if necessary, Spark plugs. Caution applies here when using interference-free plugs: double is not better here, it should then not be used with a radio interference candle, as the entire anti-interference resistance would be too high.

For an easier overview, here is a small legend for NGK spark plugs:
The letter combination before the heat value (number) gives information about thread diameter, hex key width and construction of the spark plug.
The following number indicates the heat value.
The letter following the heat value indicates the thread length.
E = long thread, H = short thread.
The letter after thread identification contains data on special spark plug construction features.
The last position, in turn a number, encrypts special electrode spacings.

Some candles have a quite short combination. No information is missing.

Here: a spark plug. If several are required, please order the corresponding quantity.