Greetings from the rabbit hole!
I remain puzzled by this one after doing some digging around.
There were indeed two patents issued to one Joseph Renshaw of Hartford, Connecticut - one being 176683 issued April 25, 1876, and later 666695 issued January 29, 1901, the latter noted at DataMP as having been manufactured by Pratt & Whitney, the former noted as "Not known to have been produced".
It is curious, then, that this unit should show up in the November 10, 1892 issue of "The Iron Age" (pp 50), as it certainly seems to match the description in the 1876 patent document.
Coincidentally, one of these sold today on Ebay for a whopping $22.95 (incl. shipping) (
https://www.ebay.com/itm/392336883947)
To further add to the confusion, an identical unit clearly stamped with a patent date of 1875 was sold on "Worthpoint" (see photos).
Occam's Razor is telling me that the April 25, 1876 patent is indeed the one that applies to this unit.
If someone else can shed any further light on this, do please let me know.
Thanks, gentlemen.
(due to size restrictions on posting, the remaining photos are in the following post)