Originally posted by Mike Murrell
I'll reference a different Bosch plug; however, the naming scheme is similar.
M103 motors use H9DC or H9DCO
The plugs with the "O" on the end have a slightly wider side electrode. It's been my experience that H9DCO plugs last a little longer than H9DC plugs.
Just found the Bosch letter designation chart.
Letter "0" designates: "Special insulator/electrode."
Does not mention what's so special about it, but that's it.