By my reading of the example it is just Insert > Float > Figure, the only difference being where the caption is placed.
On 24 October 2015 at 17:41, Nikos Alexandris <n...@nikosalexandris.net> wrote: > Dear Tufte-LaTeX users, > > the example file "tufte-book.lyx" contains an example of the "float: > Figure*", a full-width figure box. I can't trace this anywhere in the > (Insert) menus. > > Using LyX Version 2.1.4. Any help highly appreciated. > > Nikos > -- John Kane Kingston ON Canada