I would be very surprised if the chain used on trailers and caravans is any where near rated shackle capacity.
The old way of working out chain capacity was D x D x G x .3
i.e.12mm mild steel chain = 12 x 12 x 30 x .3 = 1296kg WLL or approx 4-5 times that for minimum breaking load.
An 11mm rated shackle has a WLL of 1500kg.
Cheers
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