FYI, any US made gun that was exported to a foreign country then imported back to the US must have a stamp from the company that imported it. Seems crazy but that's the law.
Several companies such as CDNN, buy used military or police guns from foreign countries then resell them here in the US. For the most part, these guns are identical to the ones that were originally sold in the US. You do find some non-standard things such as lanyard rings, different sights or grips, and odd barrel lengths. A bunch of S&W Model 10s have been on the market lately with 3" barrels that were imported from the Far East, a real oddity.
As Graybeard said, the dash number indicates an engineering change. Older S&Ws didn't have a model number stamped on their guns. Beginning in 1959, all S&W guns were identified by model numbers instead of names (like Masterpiece, M&P, etc). All previous guns and any new models always started with the basic model number such as Mod 10. When a change was made where some part was not compatible with the previous part, a dash number was issued. Most of the engineering changes were not improvements, rather a way to reduce manufacturing costs. Typically, the lower the dash number, the better the gun.
Though dash number aren't all that important, you (or your gunsmith) really need to know what dash number you have when you order replacement parts.
There are a lot of variations on the Mod 66. It is a twin of the blued Mod 19. These are some of the finest guns S&W ever made. Unfortunately, S&W discontinued them so we are seeing prices climb.
