Waterproof Enclosure Knockout Size

[faultywarrior]

Does anyone know what the correct size and thread pattern the threaded knockouts on the Aluminum Waterproof Enclosure are?  I can't seem to figure it out, despite having 3D printed several different sizes and styles of bolts; none of which seem to match up.  I figure before I waste more resin and time printing more and more test parts, I'd just ask.  I can't find any real spec sheets or drawings that would list this data, and my own measurements are inconclusive.