Helen,
I don 't know where you can get calibated imperial chain from in the UK but I am sure either Dick, Daria or Alex will be able to point you in the right direction. We just used our new 8mm g70 chain for the first time and enjoyed having almost double the capacity of chain in our locker which is very handy in deep fjords.
Simon

Hi Helen,
We had the same problem - our chain spec was 7/16th inch. I started with corresponding with the manufacturer - Ideal Windlass, who were, shall we say, somewhat ambiguous in their response. Their final response was a little longer is better than shorter

On the face of it, you are correct, that your spec should be 8mm:
5/16in = .3125in = 7.937500mm

However, the important measurement is the outside length of your chain link. We found that "calibrated" chains from different manufacturers do not necessarily have the same link length. our metric equivalent is 11.11250mm, and Ideal eventually said 12mm "should work".

I ordered 10m of 12mm chain to test from one manufacturer. It jammed on our windlass, as the links were too short. As an aside, our old chain also jammed on out Gypsy/wildcat. It had a 60mm link length. We finally found a 12mm chain with a 65 mm link length through a chandlery - incidentally at a very good price. Again I ordered a 10m test length and it ran through absolutely perfectly. The two 10m lengths are now attached to our backup rope rodes, and we have 100m of lovely new chain.

So, why the lengthy story? 8mm is the correct diameter for your Gypsy/wildcat. You just need to find a chain with the correct link length. Measure precisely what you have. Presuming that the old chain is working for you, specify that link length stating that a little longer may be acceptable. Then get a sample; it will never go to waste....

Hi Helen,
Try Maggi in Italy.
They will ship most anywhere in Europe and have a US distributor in Fort Lauderdale. For G4 they have duplicated the very popular US 5/16 G4 ACCO chain and may have done the same with the G70.
Let us know how your researches go.
My best, Dick Stevenson, s/v Alchemy

Hi Alex,
I was thinking the kellet for the conditions I was referring to: contrary currents and sometimes opposing wind (Bahamas being a prime example) needs more than a couple of pounds to keep the nylon rode from finding its way to trouble. Mine is home made from dive weights and I long ago forgot its weight, but I would say pushing 20 pounds/8 kilos. The 1-3 pounds you suggest would hardly make a dent in a nylon rode that has any real pressure on it.
My best, Dick Stevenson, s/v Alchemy

Alex, thanks for your reply. I 'm off to measure the exact sizes and then do some phone calls. Already got some samples as you 'd suggested but more effort obviously required in this direction. Will post update on any success I have. Thanks H

Thanks Dick, will follow this lead up also and keep you posted.