This Ithaca manufactured 26" long barrel is for the model M-66 20 gauge Supersingle lever action single barrel shotgun with 3" chamber and is in very good condition exhibiting a brown patina with some original blue finish in protected areas and may have scattered specks of old surface rust.  This modified choke barrel comes with a brass bead front sight, the early variation extractor (round shank) and extractor spring.   (file photos) 

Note: Ithaca model M-66 shotguns with the following year/serial numbers have been observed with this part: 51645