@Nerobro: That is very kind, but save your money. For me this method works fine and the threads didn‘t fail up to now...

@1/8 IC fan: Shapeways prints my parts with Nylon powder: https://www.shapeways.com/materials/versatile-plastic
The sinter process doesn‘t create a density like injection moulding. So forming the thread with a screw is a possible way. I also just screw the threads on all my ballcups without tapping. Delrin is maybe too strong to do it like that...