This item was dug up by a friend at an undisclosed location in Cornwall.
I believe it to be a bucket lift. This device would have been right at the bottom of the pump column immediately above a clack valve which sat on top of the windbore.
I did wonder if it had come from a hand pump such as you would see in the middle of a village but the diameter is too large. The largest I've seen was about 3 inches diameter.

Length just over 2 feet and diameter of 8.5 inches approx.
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End view
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Detail and what looks like the remains of the original leather between the outer ring and the body
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Outer ring that held the leather washer
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Shank or tang of the bucket lift showing a tapered length and keyway for fixing to the main shaft.
🔗Personal-Album-342-Image-86947[linkphoto]Personal-Album-342-Image-86947[/linkphoto][/link]

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I did a bit of research on 'Climax' deep well pumps a while back and found a blind link reference to them being used in Cornish mines, the search was motivated by a pump of around 6-8 inch bore found at a quarry in Corsham.
Perhaps the bucket assembly was part of such a pump?

🔗Personal-Album-1695-Image-86950[linkphoto]Personal-Album-1695-Image-86950[/linkphoto][/link]

🔗Personal-Album-1695-Image-86949[linkphoto]Personal-Album-1695-Image-86949[/linkphoto][/link]

I would say Roy's item is quite early.
The scarfe joint is almost identical to those found on the pump rods of the Wills Founder engine in the Peak District Mining Museum.
The joints involve two matching but dissimilar scarves that have a square sleeve hammered down over them to tighten on a slight taper.
They must have been a pig to make properly but are easy to assemble. The PDMM engine dates to 1819.