OH, ok, I was looking at the bottom of the grip handle, but on the side of the bottm strap., which that # is also on the side plate. The # on the bottom of the grip handle is 21K8***. Yes, thanks for the # to the plunger and spring. I entered "cylinder bolt and spring" in the search function and got 1000 different things. Now I know to punch in S&W K frames and pull up the schematic and it lists all the parts one can order. Also, I don't know, Jerry Kuhnhausen calls it the cylinder bolt/hammer stop and says it's a double duty piece with the front being the cylinder pivot and the back end being the hammer stop. The only thing I can figure , as far as the plastic piece behind the bolt, was that it wasn't plastic at all, but maybe glue that the factory squirted in there to keep the plunger and spring in place. The bottom of the main spring was embedded in some kind of glue, as well.
Gene
P-40
Semper Paratus