#2 of 2: Cast Iron Western Horse Stirrup

I'm guessing this an' the previous are of late 19th to early 20th C manufacture. There are small similarities; the piercing in the foot-rest portion, an' the way the horizontal upper bar is fitted with one round hole an' a larger rectangular slot. Otherwise, they are unique to each other. This one has more surface rust; both show use, but are far from being worn out. Tell me what you can about these, please!
Thanks, again, for lookin'!

 

And I didn't see that you posted a size on either one.....for an adult side boot of whatever source????

 

My grandfather owned horses and i rode every summer on trail rides of 600-2000 riders with him. I have never seen stirrups like these. I wonder if they were covered with leather at one time.

 

Some dimensions:
The cross-bar is 3 3/4" long overall, ~7/8" diameter; the slot on its upper surface is 1 5/8' x 1/4"; the hole is ~3/8" diameter. I note that the position of those two features are reversed on the other stirrup.
The stirrup is 5 1/4" high an' 6 1/4" wide; it weighs 17 3/4 ounces.
I doubt it was ever covered with leather, or anything else.

Both of these stirrups, along with my earlier post of the leather-covered one, give every indication of being designed for working saddles, including perhaps of a military service for these iron examples...an' maybe foreign, as opposed to US or CSA forces.
I have done no research, but am inclined to pursue that now, based on Aquitaine's comment (They don't look familiar at all, really! I started looking at McLellan military saddles, as some of them had metal stirrups, but didn't see any matching...), an' Larks, above.
I count few horse-persons among my acquaintances, but I'm gonna dig around among them, an' hope for some direction. Ant pertinent news will be posted right here!