I want to replace my chain and I could not find any sort of mark on the windlass to indicate what chain to use. Interestedly I did find marks on the chain itself... "G3."

So I went to WM and found this bit of quote in their "advisor:"

"The least expensive chain is called proof coil chain, or Grade 30, with G3 stamped on the links. It's what most boaters use, but will not work for windlasses, since it has longer links than other types, and a short link length works best for gypsies. Proof coil also does not have a uniform pitch (the length of the opening in each link). Use Proof Coil chain for non-windlass boats."

OK now I am really wondering...

This chain seems to work just fine in my windlass, however it is terribly rusted in places. The rust flakes off when I haul the chain and it has the potential to stain the deck... and for peace of mind I want to replace it.

How exactly do I tell what size it is... and as I mentioned it is G3 now, and seems to work just fine. Is that a bit odd or what?

I have a manual horizontal windlass.