I presume that the base supplied with a new QCTP with the threaded section is supplied oversize to enable you to machine it down into the required T nut, as I dont have a T nut for the lathe this is my main option as it already has the threaded hole for the 16mm post supplied. I need to remove a fair amount from the 2 sides so it will be hacksaw, then mill then mill 2 rebates into the top half of the nut to accommodate the thickness of the nut slot. the other option would be to start from some blank stock, then drill the 16mm hole and thread it, and then do all the steps above.