There were three different Ithaca Gun Co. hammer doubles. The first was the Baker Model which was made from the founding of the company in the early 1880s into 1887, when it was replaced by the New Ithaca Gun (NIG) at serial number 6550. The NIG was made from 1887 to 1914 and NIGs were serial numbered right along with Crass, Lewis, Minier and early Flues Model hammerless doubles. In 1915 Ithaca Gun Co. introduced a rather short-lived hammer version of the Flues called the Two-Bolt Model which used coil main-springs. With a four-digit serial number your gun is either a Baker Model or a NIG from 1887 to 1889.
There is a much better Ithaca serial number chronology in the Second Edition of Walter Snyder's book The Ithaca Gun Company -- From the Beginning. The chronology in the link above ignores the NIG and omits the Minier Model, making it pretty useless.
Last edited by Researcher; 12/19/12 11:29 AM.