This spacer is 20mm by 0.6mm, to be used with a Cana Modz spacer. I'm limited to .6mm because of layer height on my printer, however, I could probably get away with .5mm.
Center cut is 6.8mm to fit the 510 threaded atomizer.
Center cut on the full 510 file, is 9.2mm, to fit the entire 510 socket connector through the spacer.
Used FreeCAD, made some very basic cuts.