My galvanised anchor chain is crusty and rusty and will not run through the windlass smoothly because the links stick together in a kink. So, I need a replacement, but would like to confirm the size. The Whitworths website has 6mm and 8mm and larger chain. I suspect mine is 6mm short link, but the links are actually 6.9mm. The increase in diameter could be the additional zinc galvanised layer.

Here are the dimensions, as measured by vernier callipers ...
Link diameter = 6.9mm
Link outside length = 31.2mm
Link outside width = 20.3mm

* Pitch (inside length) = 18.1 mm