There is no way to tell the gauge from the serial number, and that may not even be a true serial number. Diamond Arms were made by several manufacturers for distribution by the Shapleigh Hardware Company of St Louis between the 1880s and 1940s. Anyone familiar with shotguns should be able to determine the gauge by looking at the gun, but to find the proper ammunition you should also have a gunsmith measure the length of the chamber.
It your shotgun a Model 37-S or 37-T ?
No
I saw one in 90 % condition with pitted barrel sell for $150.00
With the serial number that you provided,your Ithaca double barrel shotgun with the damascus barrels was produced in the year 1900.
Check the barrel and receiver
To identify the serial number on a Boito shotgun, first examine the receiver, as it is typically where the serial number is located. Look for a series of numbers and possibly letters stamped or engraved onto the metal surface. In some models, the serial number may also be found on the barrel or under the forend. If you have difficulty finding it, consult the owner's manual or contact the manufacturer for guidance.
look on the breach, barrel.
1896
Check the receiver and barrel
Try the receiver, barrel, forend
You may have to break the shotgun down in to the barrel section and the receiver section first.Look under the barrel section on the flat just ahead of the lug for the serial number.
Please identify the model and recheck the serial number to be sure there isn't a letter associated with it. Thank you