I needed a way to attach flags to my 55.1 PU for an upcoming parade. I came up with something I think is pretty trick. I thought I'd share this in the event someone else could make use of it.
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I modified a rubber block style stake pocket anchor. I took out the eye bolt and replaced it with some 3/8 all-thread. I threaded the inside of a short length of 1/4" water pipe. I screwed this onto the threads sticking out of the top of the anchor. The flag stick fits loosely into the other end of the pipe.

regards,
Leon