Impossible to answer without a serial number.
The frame size of a Smith and Wesson model 66 is K.
The smith and Wesson model 10 has the K service frame.
No, it is an L frame.
It is a K-frame.
K frame
The Model 13 is on a K frame.
I believe it to be the K frame
K frame
1957 to present.
1957 to 1999
I frame
N