Buy they by part number from Honda. They are an odd size, but why not? That's all the deemed necessary on the earlier bikes and the RS250.

I expect the MC21 and MC28 went to the more common M8 to save money by using a size used throughout the Honda model range. The MC16 and MC18 design is also more compact, so it's a space-saving thing too.

The RS probably used them as they are lighter. O-ring heads that are removed after every use are probably under less torque too (not positive about that, but someone will know) so a smaller stud/nut can be used. Every gram on a GP bike counts.
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Andy.
NSR-WORLD.COM

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