[carguychris]

While I don't take issue with what's been posted so far, I would like to point out that dash numbers have sometimes been used to designate options, generally barrel lengths and types.

For instance, the Model 36 no-dash had a 1-7/8" or 3" tapered barrel, whereas the Model 36-1 was the same gun with a 3" heavy barrel, and was sold simultaneously (more about the Model 36 below). Another well-known example is the Model 10-5, which had a 2", 4", 5", or 6" tapered barrel, and the M10-6, the same gun but with a 4" heavy barrel.

It should also be noted that S&W was not always consistent about changing dash numbers when engineering changes were made. Arguably the most well-known example is the Model 36, which was produced from 1957 until the mid-1980s in no-dash / dash-1 form despite the fact that numerous changes were made during that time, most notably the deletion of the barrel pin in 1982.