1/8 od is common size. Sometimes the holes get egg shaped before the rivets pop and then you have to use the next size up. If you are having too many pops, it is likely that your axles are shot or you are abusing the trailer with: too stiff suspension on your truck or your road/speed is too rough.
You can get the OEM rivets (colored white) from JC. They come in packages of 25 (as I recall). Just call 937-596-6111 and use the option for service/store/tour - Amy will gladly send them out to you.
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