You can either go to Honda and buy whatever they sell you at a vast amount of money, or fit whatever your local dealer has in stock. I have two different caps on mine, as the front wore through under braking during racing...
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MC21SP Plaything
BMW F800GS Bumblebee
Triumph 9551 Daytona Big boys toy
FJ1100 Sporting relic
GTS1000 oddball