if it's a 1911 45 cal. military pistol it was made in 1918 by Colt
Look in "The Ithaca Gun Company - From the Beginning"
1916-fluse model
made about 1943 by ITHACA firearms company
about 1945
about 1917
made in 1945
Your serial number indicates that your Ithaca shotgun was made in the year 1920.
The Ithaca 45 m1911a1 serial number NO 860361 pistol was made by Ithaca in 1943
You would need to include the model number or name of your Ithaca firearm,along with the serial number to get the correct answer.
A model 37 with the serial # 10464 was produced in 1939.
Your serial number indicates that you have a Ithaca crass model double,that was made in 1903.
It sounds to me that you have a Ithaca Flues model double barrel shotgun.With the serial number that you provided,your shotgun was made by Ithaca in 1917.