Wow I want that flooring in my new addition! and you have it in a shop!,,Thanks guys for all the advice, it's been epic It was a 3/8" UNC bolt x 4.
And just to prove it, and the most boring photo of the year .... yay
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good job on the wheels. At our local Canadian tire. They have a screw board with every possible nut and screw on display so you can try each one trial and error.