Our shop foreman recommends the Bosch W7DTCs for both the Digijet (1.9L) and the Digifant (2.1L) EFI systems. Originally, VW called for Bosch W7CC0, if I recall correctly. These plugs are obsolete, or nearly so. I have the W7DTCs in my 1984 VW Vanagon Westalia.
Spark plugs use SAE and not Metric. The one that fits it is the one that fits it.
If the Shoe Fits - 1990 TV is rated/received certificates of: Argentina:13 Australia:PG Iceland:L USA:PG
Chanpion RJ19LM
18MM
Other spark plug brands which cross-reference/interchange with the Champion QC12YC include: NGK: BCPR5ES Denso: Q16PR-U As for what applications the spark plug fits, it fits various European applications, such as BMW, Mercedes, and Saab.
5/8"
Champion J8C
Rj19lm
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1990 through 1998
18 mm
Autolite 258