Cap that fits around the short M42 male thread on most ZWO ASI cooled cameras. The cap that comes with the camera only fits when the 11mm spacer ring is on the camera, which needs to be removed when using a filter wheel or filter slider (in my case, all the time). This prevents getting dust and dirt on the glass window. Has an "edge" for easy gripping when removing.
In Cura, make sure to "optimize wall printing order" I also use "Combing mode: not in skin"