Thanks to efwoodworks for posting this on the forum.

I recently acquired a Stanley block plane with a cam-lock cap. I noticed the casting stamp on the Stanley cap matched one of my Millers Falls plane. Turns out the #16 Millers Falls had a Stanley cap.
Millers Falls uses the same cam-lock cap on the #16, #17, #57 and #75 with a black finish and #26 and #27 with a nickel finish. The casting number on these caps is 344 but the majority of the caps I’ve seen have the number covered from the japanning.  Visually you can tell the difference with Millers falls having a round center support in the cam lever and Stanley having a long curved top center support.
Functionally, either cap works great. This is for anyone who wants to make sure they have the correct cap on their plane.   I’ve included a picture with the Stanley on the right and the Millers Falls on the left.

Millers fall – Stanley block plane cap comparison