Using "diti" as plural means considering each individual finger in the group, whereas "dita" means all the fingers as a sole entity (http://www.treccani.it/enciclopedia/diti-o-dita_(La_grammatica_italiana)/). "Diti" is no longer used and if you use it in a conversation chances are that it will be pointed out as a mistake.
Collectively: "le dita della mano" = "the fingers of the hand"
Individually: "i diti indici" = 'the index fingers"; "i diti medi" = "the middle fingers"; "i diti anulari" = "the ring fingers". My web source "Centro Studi Italiani" www.locuta.com/2plurali did not have a word for "the little fingers"; I could not find it in Reverso, either.