Number of screws
When talking K/N frame Smiths, the conventional discussion of 3,4 and 5 screws generally covers the postwar changes, which were as such:
5 screw guns - 4 sideplate screws, one trigger guard screws - up to about 1957/58.
4 screw guns - 3 sideplate screws, one trigger guard screws - roughly 57/58 to 1961/62
3 screw guns - all sideplate, post 1961/62.
Because these guns have been made for over a century, any discussion about the number of screws needs to be tempered with the timeframe for the piece.
By this, we need to remember that there were "pre-5 screw, 4 screw" K frames. Yes that's right, the original K frame hand ejectors - Model of 1899, had 4 sideplate screws but NO trigger guard screw. So, technically you can call these 4 screw guns, with all the screws on the sideplate, but again - when folks generally talk about 4 screw guns they are talking about the ones in the late 50's to early 60's.
As well, the recent manufacture of special guns from the Performance Center have included several "4 screw" sideplate guns, but there is no trigger guard screw.
Now, we won't even talk about the 6 screw J frames guns. Another example that the standard is that there is no apparent standard.
.................SmithNut