What he studied experimentally with the buttons and threads is know in graph theory as the "Giant component" threshold and is exactly known.
https://en.wikipedia.org/wiki/Erd%C5%91s%E2%80%93R%C3%A9nyi_...
https://en.wikipedia.org/wiki/Erd%C5%91s%E2%80%93R%C3%A9nyi_...