Mount is hard plastic. No amount of “give” - at all! Not flexible. Internal diameter 17,6 mm. Microphone has a diameter of 20,9 mm (or 12,7 mm on the thin part).
No amount of violence will allow the mount to be fixed on the microphone, if the aim is, that the microphone survive. I use a Røde M5 microphone mount instead. Someone in Superlux purchasing department has demonstrated complete ignorance and probably only looked at price.