While I have been going through rolls of nickels, I have pulled quite a few 1939 dated nickels. After learning about the two hubs used that year, I wanted to find a way to tell if the nickel I find is a rev of 38 or 40, especially the 39-d and 39-s. So here is what I have found is an easy way to tell the two reverses apart on coins worn down below XF, where you cant see any steps. First, I'll explain to anyone who doesn't know about the reverse types how to tell them apart on an Uncirculated coin or one that has very little wear. On the Reverse of 1938, the steps are cut somewhat unevenly, some have said that they are wavy. Any nickel minted in 1938 is a reverse of 1938. (well, not all nickels, there were buffalo nickels minted in 38) The Reverse of 1940 was put into service in 1939 at Philly first, and only a small amount of the 1939 nickels made there are of the reverse of 1938. On the Reverse of 40, the steps have been straightened and cut deeper, and a line has been engraved on both sides of the steps, giving them an ending point on both sides. These details are easy to see on any MS or XF and above coin for the most part, but if you have a coin in any grade below that, if you use step details to tell the reverses apart, you have a problem, no more steps! I looked over a number of coins and found a marker that you can use to tell the reverses apart. Look on any 1938 Jefferson, which will be Rev of 38. Look at E Pluribus Unum on the reverse and pay special attention to the S in EPU. There is no serif at the top of the S. Now look at any 1940 dated nickel, which should be all Rev of 1940 except for the 40 proof rev of 1938. Look at the same place, the S in E Pluribus Unum. You should see a serif at the top of the S. Use this marker to properly ID the reverse type. Check out PCGS website for high quality photos of the same coins.