Looks like a pin from 1911 hammer strut assembly.
Interesting.
Laying the pin across the back of the hammer, between the frame sides, it's a good fit lengthwise.
But, I did not take the pistol down that far and the hammer seems to cock, lock, and release normally.
Then I'd say it is not from a GM!
Barney
Just curious if the mystery pin ID was ever solved?
His wife/girlfriend put it there.