The F marking on the area (receiver water table?) means the grade F- Field. Ithaca chokes are designated on the barrel flats, using a numerical system: ergo: 1 cylinder/skeet choking 2 modified choke 3 improved modified and 4- full choke.
You can also date the NID series Ithacas from either the presence of the cocking indicators on the receiver topside- from about 1925-to 1933- the NID series had those, if the pins are up, the hammer is cocked- if the pin is down flush, the hammer is down-- After 1933, Ithaca deleted this feature-- Hope this helps-- RWTF
