Hi I spoke to keg king and asked them this direct question and they wouldn't / couldn't answer it.
I measured the one in my fermentasaurus and ordered some replacements just in case from aliexpress.
These are the dimensions measured with a vernier gauge
Oring in the butterfly housing ( note goes on the vessel side of the valve)
47.75mm external 41.75 internal so the oring is 3.1mm diameter (give or take)
I went for a 48mm one from here
https://www.aliexpress.com/item/4000867504808.html?spm=a2g0s.12269583.0.0.5f3b5b31pdprl8
O ring against Pet bottle
36mm external 29.5mm internal so 3 - 3.5mm thick oring
I went for a 36mm one of these
https://www.aliexpress.com/item/4000867525443.html?spm=a2g0s.12269583.0.0.6f6a38e68nOjyK
O ring inbetween butterfly housing and Ferment vessel
26.75 external and 22 internal so about 2mm diameter oring.
Went for a 26mm rather than 27 here not sure why, think it was because it sits in a groove and easier to stretch into the groove than reduce size
https://www.aliexpress.com/item/4000867504808.html?spm=a2g0s.12269583.0.0.14825b31zfybW4
When you look at the websites they aren't the exact figures that I measured but the orings have variance with being squeezed etc when I measured them.
I ended up ordering keg post orings as well as they were so cheap in packets of ten.
Hope this helps.