A search of the yellow pages for a speedo repair shop in your area will probably find you what you need. I don't know what the back of your needle or front of your speedo look like but failing that, you may be able to fill the back of the needle with epoxy, let it dry then use a tiny drill bit (the hardware store should be able to help you here) to drill a hole in the epoxy slightly smaller than the hole. You then push the needle onto the shaft. By far the best bet is the speedo shop. Good luck.

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Name your dog Naked so you can walk Naked in the park.