Every other ERYONE spool I have found uses ISO threads, which are difficult to print cleanly with PETG as they have a 60° overhang. This generally causes issues with internal threads as the filament may not bond to the lower layer and spider web over to another point in the arc. 

To combat this, I created this spool. It has 45° trapezoidal threads so it can easily be printed quickly at large layer heights without overhang issues.

This is a no frills spool, with holes on only one side. The core is just a bit smaller than needed, but screwing the sides together will put pressure on the cardboard core. I would also suggest snipping off the excess filament in the core so it can let go at the end of the roll without issue.

I have uploaded a customizable version so users can adjust the spool based on the cardboard spool they replacing. 

Core Widths of 70-80mm should work without issue. 

Larger or smaller will have issues as I cannot make thread size selection customizable