I got this from the father in-law,

but I was not convinced on his thoughts on this tool. Any ideas? Thanks.
To me, that is an I.D. plug; back the wing nut off, stick it in a quantified hole diameter, tighten the wing nut, the rubber biscuit swells.
It is also interesting in design; the end cap appears to be a pipe cap, with implications that the bolt/shaft is a piece of pipe with O.D. thread of what pitch?/wing nut for sure & possibly the end plate must have the same thread.
Why the long length of the bolt/pipe and the excess O.D. thread length; begin to sense homemade for a specific application. Cramped space; need reach - not too plausible as still have to turn the wing nut with your hand or a tool. Hold the bolt/shaft true with your left hand and tighten the wing nut with a soft hammer?
Probably not a high use tool, but maybe there could be some usage mark clues on the wing nut etc.; is the end plate threaded or welded on?
Cool find!