Size.
The main difference is that the TSW slide and frame were made as a matched set and have the same assembly number on each.
39 holds less rounds then the 59
The frame size of a Smith and Wesson model 66 is K.
The smith and Wesson model 10 has the K service frame.
take the grips off
The frame.
The Smith and Wesson K frame revolvers were made from 1946-1983.
The M19 is a medium size K-frame. The M28 is a large size N-frame, which was also used in producing the 41 and 44 magnums.
Standard Catalog of Smith and Wesson Firearms by Supica and Nahas History of Smith and Wesson by Jinks.
Next smallest to the X frame.
No, it is an L frame.
K frame