What is This Thing?

Looks like a hitching post top....

The lead piece makes me believe it is used as a weight, too small for a boat anchor, but possibly for a line to measure water depth.

Is the bell-shaped thing solid?

Not a hitching post thing.

Could be a line weight, but I doubt it.

The bell shaped lead is solid.

It might be a mason's tool for keeping a level line taut. Tie a string to the ring and hand it off the end of the block wall you are building to keep the courses level.

'hang it off' , not hand it off

looks to be something for cable/rope/string management.

Could be a diving weight...for spearfishing

It is a "service bell" pull. Maybe.

Does the post attached to the lead section retract when the lead piece is pulled outwards. Almost looks like a slide collar that locks into place along a shaft by that pin.

Kind of looks like a nose ring for a bull or a pig.

Bull Shannon never wore a nose ring that I am aware of.

But yes, a nose ring, the lead weight is there for ??? to keep the bull's nose down?

Could be a weight they used with balance beam scales for cotton or something....

By Jove, I think you've got it! It reminds me of a Middle Eastern market where spices and herbs are sold, and the scale weights are fairly small.

Yeah, OK, they use that in China, and a lot of other places in Asia also.

I found this

"Late 19th Century 1lb. weight of blancmange quatrefoil form"

But it's all iron. Can't imagine what the "blancmange" bit is all about.

I imagine it's because the shape resembles a blancmange mould (US mold) of the sort popular in those days.

white desert or rather "white dish", some have proposed "bland dish", the recipe varies according to local custom. Quatrefoil is a Christian symbolic design. If someone offers the blancmange quatrefoil form to the sick it is a "get well soon" gesture, in the name of Jesus. Who knows if it always worked?

that an iron 1 Lb. weight should be made in this form is illusory of an honest business transaction, i.e. honest weights and measures.

Looks a lot like a duck decoy anchor I have seen used.

Wrap the line around the decoy for storage, hang the ring around the neck of the decoy to keep it from unwinding.

I call that plausible also.

Given the location, the loft of a very old barn in South Dakota, I'd say that is the most plausible answer, yet. Using my digital bathroom scale, it comes up at one pound, even.

I give you a GA, if allowed.

Maybe it's a weight for a fishing net. The ring appears large enough for a diver to easily pass a line through.

Could be a gate weight to keep the gate or maybe a screen door closed...possibly a chicken coop door...