I am afraid you will get here only advice but not a definitive answer.
You may try your old chain on the windlass and find out if it works properly or not.
If it does - just use the link size to check the new chain.
If old chain does not work well - it is a hint that the other 10mm link should work. However, to be sure, you may check the printed manual, ask the manufacturer, take the gypsy to the store or ask the seller to visit the boat.
Other consideration, after ascertaining proper link size, will be the tensile strength of the chain (higher the better of course), and highly related to the strength - weld quality.
Meir Riba
+97254427780
eldadhadani@...
meirriba@...
Sent from
Meir Riba