I’m surprised the web site does not say which rockets this will fit in.
I would go as far as saying this looks specifically designed for the Starships payload dimensions, 8m dia by 17m. Baring in mind that the front ~7m are in the nose cone of the rocket.
I think it's quite sensible for a startup to be working on space station designs that are utilising the expected capability of starship.
https://gravitics.nyc3.digitaloceanspaces.com/StarMax_One_Pa...
See payload section on: https://www.spacex.com/media/starship_users_guide_v1.pdf