Franklin corresponded from time to time with Sir Francis Dashwood, the founder of the Order of the Friars of St Francis of Wycombe, the most infamous of the hellfire clubs. There is no evidence that Franklin actually was a member of the club or partook of its activities.

[1] https://www.nytimes.com/1972/02/27/archives/the-hellfire-clu...

[2] Ashe, Geoffrey. The Hell-Fire Clubs: A History of Anti-Morality. Great Britain: Sutton Publishing, 2005, p. 121