These are modified to fit the foldable headband here,
https://www.printables.com/model/1277291-foldable-length-adjustable-koss-ksc75-headband-tra
Download the original files jimthing_2000 built if you want to attach them to the original Sennheiser PX100 headband
The author remixed this model.
The caps are modified to fit the custom headband above. Original design without any modifications can be found here (credits to jimthing_2000);