Where type is hand set, the type is kept in trays. Among the boxes in the lower-case trays are ones for the ligatures (letters joined on a single piece of type) ff, fi, fl, ffi and ffl. Of these, the ligature ffl always looks the newest because it is used least often. Just how infrequently is it used? When I asked the editor, he informed me that Kucera and Francis's million-word sample of text published in the United States in 1962 revealed only 87 occurrences: ffl occurs, on the average, in only one word in ten thousand in running text.
"Word Containing the FFL Trigram,"
Word Ways: Vol. 24
, Article 16.
Available at: https://digitalcommons.butler.edu/wordways/vol24/iss2/16