I have four different flags for my trike. They all have the same kind of base as a starting point. I have a standard orange triangle for my road riding. I have a Catrike flag that is a wind sail style. And I have Wisconsin and US Flags. The last two are mounted to the pole with glue. To mount to the trike, I installed two rubber washers. One of them flat the other a cone shape. I just slip the flag onto that. A bit further up I use a short double sided velcro strip(Menards have them) to secure the flag. It's an easy and cheap connect/disconnect.
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"The difference between genius and stupidity is that genius has its limits."
-- Albert Einstein