I'll be installing a set of Beru S1K Silverstones in my twin turbo M103.
The Silverstones were a non resistor plug with a solid silver electrode.
I don't think they are still available from Beru but they were intended to be used in high performance engines and had a variable heat range design.

They may be still marketed under the Nology brand.

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1971 280SL ROADSTER
1988 300CE TWIN TURBO WIDEBODY
1994 E320 CABRIOLET
1999 C43 AMG
2005 G55K AMG
2008 CLK63 AMG BLACK SERIES