A nice carriage wrench with nut-retaining feature was made in 1885 by Roswell Cook in Ilion, NY.

I cant see how the heck this thing works, does that arm pivot to hold the nut, it seems to me the two bottom pict. shows a different wrench, I can see where it might swivel on bottom pict. but cannot see the little rivet on the middle pict.

One squeezes the little arm on the bottom upward against the main body of the wrench which pivots the nut-locking other end of the little arm inward into a shaft on the inner side of the square end. I believe the maker left a bar for the arm to pivot around in designing this wrench. This would eliminate the need for a pin. After inserting the arm piece into the wrench body, the maker then pinned the heavy spring to the top surface of the wrench.