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[pat1098]

These are often referred to as an SKF nut.

The one on the lower pulleys on the half-time or cross-over shaft is the same as on older 2-valve models.

The ones on the cams are larger, and only come on the later 4-valves.

 

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[pat1098]

If you have a good socket, and the nuts aren't too damaged, you can re-use them, if you use the appropriate Loctite (about 242, the red one).
I mean, you are supposed to replace them, and I usually do on a customer's bike, but I have run the odd 'dog-eared' one on my own.
They are made of pretty soft material.
I don't know about getting them from a hardware store here, but you may be able to find generic ones from a fastener specialist or a bearing supplier who deals in SKF bearings.

 

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