Obsesed with Doubles, Rocketman above describes the engineering aspects of threads as stress risers clearly.
As for the original post and pics. there is no difference in the internal parts attributable to the number of screws. There seems to be lots of screws because each screw (pin) has a locking screw beside it, presumably to stop it coming loose from the swivelling motion of internal parts that are anchored on the screws. The plain axles in the bottom pic correspond to the main large screws in the top pic, which is to say two, one for the tumbler and one for the sear.
What is more interesting is that the guns in the pics are OUs built on Anson-Deeley type actions. The maker managed to make room inside an OU action to house the AD bits. It would be interesting to see a top down pic to get an idea of the width of these actions. Something tells me that they are wider than most OUs.
