These were born out of playing around with the idea of printable directional props. I realized that the project could easily be adapted into making drag discs that have a prop-like look to them but remain durable. These are intended for printing with Taulman's PCTPE filament for a press-fit durable piece.
(pictured here dyed blue because I got a bit experimental)
The bore diameter ends up being, with my printer and PCTPE, a press-fit on a 1/8" shaft. I've been battling the last few months with mine and they have not shifted at all, despite having spent some time hung up drag prop to drag prop on another ship.
An earlier printed set with a thinner disc is on Greg's Provence and has held up just fine.