The easiest way to tell is the date. Most Crane sinks have the date of manufacture cast into or embossed into the fixture. Usually there is a Star shaped logo printed on the fixture that will also mention the Model of the sink. The model name can be extremely helpful!
Once you’ve determined the date of manufacture, look at the appropriate section to find the part you need. We’ve not been able to find any Crane sinks that were manufactured between 1942-1946, so we consider that to be the War years. Anything before 1942 is prewar, anything after 1948 is postwar.