The third grounding pin seems to be always round and with no taper in any
sense. The socket I have here has a ground-pin recess that is a conflation
of a semicircle and half a square in cross section . Equally solid, ie no
springing action. Or is there a taper down the length of the ground pin
recess that I cannot gauge . I expected a round pin with a tapered flat and
a slot along the length of the pin to give some sprung gripping/ latitude
for dimensional inconsistency.

While at it, are the holes in each flat pin , for anti-tugging latch pins ?