Help identifieng this

[steve2]

Clearing out my wife’s uncle house and we have come across this item.
We haven’t a clue what it is but he was into boats, travelled extensively as her was a British consulate.
It is heavy and i think it is cast iron and about 8” round

[rallye101]

It looks cool, I want one..... I have no clue!

[twing]

Manilla - https://en.wikipedia.org/wiki/Manilla_(money)

Cool thing!

[steve2]

That is brilliant thank you

[twing]

I’d love to say I knew all about them but Google reverse image did that.interesting thing to own

[Super Sonic]

Looks like some sort of retaining plunger.