I know this is an old thread but since I was trying to get the part number so I could order some more, I figured I would add to the answer.

The RS250 part number could be correct, but I wanted to double check it against the plugs I have been running all year in my MC28 race bike. The NGK plugs I am using are part # NGK R5300A-105. They are about $22.00 each (much cheaper then the $36.00 RS 250 plugs).

Thanks,
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Charles Gallant