Forgive my ignorance, as I've not read through the whole thread, but are you basically after a 5" wheel with a 3/8" UNF nut attached to fit to a drill motor? If so, I've got a couple of homemade wheels from the previous incarnation of Drumroll still kicking about. They're 5" (give or take a smidge as they have bike tyre screwed on and it's worn a bit) and I welded a UNF nut onto a couple of pieces of steel which then bolt to the HDPE wheel. They're not pretty and they're not entirely concentric (so they wobble a little but nothing noticeable in the arena) but if they would be of use to you, let me know and I'll dig them out. Will be back in my workshop next week.

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