The K-frame is the second smallest frame size that Smith & Wesson manufacturers. The first K-Frames were produced in the Hand Ejector Model of 1899, chambered in 32/20 and 38 Special, which is still in production as the Model 10, or Military & Police model. Though there have been many changes to the 38 Hand Ejector to evolve it into todays Model 10, the basic K-frame is still the same.
As a bit of trivia, the first 357 Magnum handguns were built on the N-Frame in 1935, while the K-frame version had to wait until 1954.
Currently the K-frame revolvers are offered in the following chamberings:
Model 10 (blue) Model 64 (Stainless) 38 Spl Model 13 (blue) Model 65 and 65LS (Stainless) 38 Spl/357 Mag Model 14 (blue) 38 Spl Model 15 (blue) Model 67 (Stainless) 38 Spl Model 19 (blue) Model 66 (Stainless) 38 Spl/357 Mag Model 617 (Stainless) 22 LR