My welding mask's plastic nuts cracked so I had to replace them. These ones include an M6 nut that is more durable. Also they are large enough to be easily turned while wearing welding gloves.
Check instructions for more info :)
The parts in the image are sliced with Slic3r, printed with 0.2mm layer height in PLA (gray) and ABS (orange). The final dimensions are 36 mm diameter and 18 mm height with a hex hole made to fit an M6 nut.
I've included the FreeCAD source so you can modify it for any nut size you want.
WARNING: STL is exported in mm. You'll have to scale down 25.4 times (0.03937 or 3.937%) if you want to print it in inches.