Sal,
This has updates:
USE OF FLAT LATCHES
The 1st style flat latch began exclusively on the Baby J frame; (earliest known #111 presented by S&W to Col. Rex Applegate), used on most all after ~ #117 in very late 1950. The only other model to have used the 1st style was the alloy K frame, never on the I frames. The Baby J frame in the high 25,000 range, began a transition to the 2nd style flat latch in 1953.
The I frames used all four styles of the standard thumb piece before beginning use of the flat latch, starting with the Improved I frame (coil mainspring) - 2nd Variation (with ramp sight and barrel rib) in 1953; above # 60430X on the .32 I frames, and at around # 747XX on the.38 S&W .38/32 I frames.
There are no Improved I frame .22/32s neither 1st or 2nd I frame variations; so for the .22/32s, the coil spring and 2nd style flat latch began with the Model of 1953 New I frames.
So all Models of 1953 New I frames and New J frames were introduced using the 2nd style flat latch. A transition to the 3rd style flat latch began in the late 1956 period for all I and J frames until discontinued on all models in 1966.
THREE STYLES OF FLAT LATCHES:
1st style flat latch; convex surface and very slight ramp towards the front:
2nd style flat latch* began on the Improved I frames, K frame airweights, and Baby Js just prior to the Model of 1953 New J frames shown here; higher ramp and flat face:
*two-bit cowboy has identified a 4th style or sub variation of the 2nd style; same shape but with only 8 serrations.
3rd style shown on lower .38 Chief Spl. in first photo, with steeper incline at the front, and in 2nd photo; also used on Model of 1953 New I and New J frames, and K frame Airweights beginning mid late '50s; ending in 1966.
Photo by Watchdog
TWO STYLES OF FL and STANDARD THUMB PIECE LATCH BACKS – SPLIT AND SOLID:
I & J frames:
All pre flat latch thumb pieces are split.
flat latch have split backs.
All standard thumb pieces post flat latch are non-split after 1966.
K frames:
I have no flat latch K frames but most likely they are split based on the I & J frames above.
All my '50s K frame standard thumb pieces are split until about the 1980s.
All non-pinned barreled Ks I have (earliest is 1980) are non-split.
N frames (never used flat latches):
All my '50s models are split. I have no N frames newer than 1956.
NOTE: Flat latches have been changed by owners due to their dislike, non-traditional looks or both. Of course the bolt it's attached to, required replacement w/the FL type bolt.
