From BiblePortal Wikipedia

International Standard Bible Encyclopedia [1]

fin´gẽr (Hebrew and Aramaic אצבּע , 'ecba‛  ; δάκτυλος , dáktulos ): The fingers are to the Oriental essential in conversation; their language is frequently very eloquent and expressive. They often show what the mouth does not dare to utter, especially grave insult and scorn. The scandalous person is thus described in  Proverbs 6:13 as "teaching" or "making signs with his fingers." Such insulting gestures (compare e.g. the gesture of Shimei in throwing dust or stones at David,   2 Samuel 16:6 ) are even now not infrequent in Palestine. The same habit is alluded to in  Isaiah 58:9 by the expression, "putting forth of fingers."

The fingers were decorated with rings of precious metal, which, with other jewelry worn ostentatiously on the body, often formed the only possession of the wearer, and were therefore carefully guarded. In the same way the law of Yahweh was to be kept: "Bind them (my commandments) upon thy fingers; write them upon the tablet of thy heart" ( Proverbs 7:3 ).

Figurative: In  1 Kings 12:10 and   2 Chronicles 10:10 Rehoboam gives the remarkable answer to his dissatisfied people, which is, at the same time, an excellent example of the use of figurative language in the Orient: "My little finger is thicker than my father's loins," a figure explained in the next verse: "Whereas my father did lade you with a heavy yoke, I will add to your yoke: my father chastised you with whips, but I will chastise you with scorpions." The Hebrew word used here for little finger is קטן , ḳōṭen , literally, "pettiness," "unimportant thing."

The "finger of God," like the "hand of God," is synonymous with power, omnipotence, sometimes with the additional meaning of the infallible evidence of Divine authorship visible in all His works ( Psalm 8:3;  Luke 11:20 ), especially in His law ( Exodus 8:19;  Exodus 31:18;  Deuteronomy 9:10; compare  Exodus 32:15 ,  Exodus 32:16 ).

The finger or digit as a linear measure is mentioned in  Jeremiah 52:21 (Greek daktulos  ; Josephus, Ant , VIII, iii, 4). It is equal to one finger-breadth, 1/4 of a hand-breadth (palm) = 18, 6 millimeters or .73 inches.