6906...SS double stack. 6904...blue double stack.
3913...SS single stack. 3914...blue single stack.

Same guns...different mags. Go figure! There is probably a reason but that is why Smith came up with the Wiz Wheel. I have never taken the time to chart the model numbers of all of the 3rd gens but the numbers are all over the board! I use my SCSW regularly when referring to Smith autos.

The upside of this numbers battle is that no matter what you wanted in a semi-auto during that time...Smith made it!